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Merge pull request #18718 from schmee/bounds
Add upperBound, lowerBound, and equalRange
This commit is contained in:
Andrew Kelley
GitHub
commit
ba8375328c
268
lib/std/sort.zig
268
lib/std/sort.zig
@ -399,6 +399,13 @@ test "sort fuzz testing" {
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}
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}
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/// Returns the index of an element in `items` equal to `key`.
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/// If there are multiple such elements, returns the index of any one of them.
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/// If there are no such elements, returns `null`.
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///
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/// `items` must be sorted in ascending order with respect to `compareFn`.
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///
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/// O(log n) complexity.
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pub fn binarySearch(
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comptime T: type,
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key: anytype,
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@ -502,6 +509,267 @@ test "binarySearch" {
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);
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}
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/// Returns the index of the first element in `items` greater than or equal to `key`,
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/// or `items.len` if all elements are less than `key`.
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///
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/// `items` must be sorted in ascending order with respect to `compareFn`.
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///
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/// O(log n) complexity.
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pub fn lowerBound(
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comptime T: type,
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key: anytype,
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items: []const T,
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context: anytype,
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comptime lessThan: fn (context: @TypeOf(context), lhs: @TypeOf(key), rhs: T) bool,
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) usize {
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var left: usize = 0;
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var right: usize = items.len;
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while (left < right) {
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const mid = left + (right - left) / 2;
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if (lessThan(context, items[mid], key)) {
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left = mid + 1;
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} else {
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right = mid;
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}
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}
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return left;
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}
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test "lowerBound" {
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const S = struct {
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fn lower_u32(context: void, lhs: u32, rhs: u32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_i32(context: void, lhs: i32, rhs: i32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_f32(context: void, lhs: f32, rhs: f32) bool {
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_ = context;
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return lhs < rhs;
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}
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};
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try testing.expectEqual(
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@as(usize, 0),
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lowerBound(u32, @as(u32, 0), &[_]u32{}, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 0),
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lowerBound(u32, @as(u32, 0), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 0),
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lowerBound(u32, @as(u32, 2), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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lowerBound(u32, @as(u32, 5), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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lowerBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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lowerBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 7, 7, 7, 7, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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lowerBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 8, 8, 8, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 5),
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lowerBound(u32, @as(u32, 64), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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lowerBound(u32, @as(u32, 100), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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lowerBound(i32, @as(i32, 5), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(usize, 1),
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lowerBound(f32, @as(f32, -33.4), &[_]f32{ -54.2, -26.7, 0.0, 56.55, 100.1, 322.0 }, {}, S.lower_f32),
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);
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}
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/// Returns the index of the first element in `items` greater than `key`,
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/// or `items.len` if all elements are less than or equal to `key`.
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///
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/// `items` must be sorted in ascending order with respect to `compareFn`.
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///
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/// O(log n) complexity.
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pub fn upperBound(
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comptime T: type,
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key: anytype,
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items: []const T,
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context: anytype,
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comptime lessThan: fn (context: @TypeOf(context), lhs: @TypeOf(key), rhs: T) bool,
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) usize {
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var left: usize = 0;
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var right: usize = items.len;
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while (left < right) {
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const mid = (right + left) / 2;
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if (!lessThan(context, key, items[mid])) {
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left = mid + 1;
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} else {
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right = mid;
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}
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}
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return left;
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}
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test "upperBound" {
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const S = struct {
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fn lower_u32(context: void, lhs: u32, rhs: u32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_i32(context: void, lhs: i32, rhs: i32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_f32(context: void, lhs: f32, rhs: f32) bool {
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_ = context;
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return lhs < rhs;
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}
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};
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try testing.expectEqual(
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@as(usize, 0),
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upperBound(u32, @as(u32, 0), &[_]u32{}, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 0),
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upperBound(u32, @as(u32, 0), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 1),
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upperBound(u32, @as(u32, 2), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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upperBound(u32, @as(u32, 5), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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upperBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 7, 7, 7, 7, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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upperBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 8, 8, 8, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 3),
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upperBound(u32, @as(u32, 8), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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upperBound(u32, @as(u32, 64), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 6),
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upperBound(u32, @as(u32, 100), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(usize, 2),
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upperBound(i32, @as(i32, 5), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(usize, 1),
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upperBound(f32, @as(f32, -33.4), &[_]f32{ -54.2, -26.7, 0.0, 56.55, 100.1, 322.0 }, {}, S.lower_f32),
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);
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}
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/// Returns a tuple of the lower and upper indices in `items` between which all elements are equal to `key`.
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/// If no element in `items` is equal to `key`, both indices are the
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/// index of the first element in `items` greater than `key`.
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/// If no element in `items` is greater than `key`, both indices equal `items.len`.
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///
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/// `items` must be sorted in ascending order with respect to `compareFn`.
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///
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/// O(log n) complexity.
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///
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/// See also: `lowerBound` and `upperBound`.
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pub fn equalRange(
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comptime T: type,
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key: anytype,
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items: []const T,
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context: anytype,
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comptime lessThan: fn (context: @TypeOf(context), lhs: @TypeOf(key), rhs: T) bool,
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) struct { usize, usize } {
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return .{
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lowerBound(T, key, items, context, lessThan),
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upperBound(T, key, items, context, lessThan),
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};
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}
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test "equalRange" {
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const S = struct {
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fn lower_u32(context: void, lhs: u32, rhs: u32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_i32(context: void, lhs: i32, rhs: i32) bool {
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_ = context;
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return lhs < rhs;
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}
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fn lower_f32(context: void, lhs: f32, rhs: f32) bool {
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_ = context;
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return lhs < rhs;
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}
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};
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 0, 0 }),
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equalRange(i32, @as(i32, 0), &[_]i32{}, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 0, 0 }),
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equalRange(i32, @as(i32, 0), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 0, 1 }),
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equalRange(i32, @as(i32, 2), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 2, 2 }),
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equalRange(i32, @as(i32, 5), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 2, 3 }),
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equalRange(i32, @as(i32, 8), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 5, 6 }),
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equalRange(i32, @as(i32, 64), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 6, 6 }),
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equalRange(i32, @as(i32, 100), &[_]i32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 2, 6 }),
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equalRange(i32, @as(i32, 8), &[_]i32{ 2, 4, 8, 8, 8, 8, 15, 22 }, {}, S.lower_i32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 2, 2 }),
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equalRange(u32, @as(u32, 5), &[_]u32{ 2, 4, 8, 16, 32, 64 }, {}, S.lower_u32),
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);
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try testing.expectEqual(
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@as(struct { usize, usize }, .{ 1, 1 }),
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equalRange(f32, @as(f32, -33.4), &[_]f32{ -54.2, -26.7, 0.0, 56.55, 100.1, 322.0 }, {}, S.lower_f32),
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);
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}
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pub fn argMin(
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comptime T: type,
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items: []const T,
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