| ... | ... | @@ -5,6 +5,67 @@ const mem = std.mem; |
| 5 | 5 | const math = std.math; |
| 6 | 6 | const builtin = @import("builtin"); |
| 7 | 7 | |
| 8 | pub fn binarySearch(comptime T: type, items: []T, comptime compareFn: fn (val: T) math.Order) ?usize { |
| 9 | if (items.len < 1) |
| 10 | return null; |
| 11 | |
| 12 | var left: usize = 0; |
| 13 | var right: usize = items.len - 1; |
| 14 | |
| 15 | while (left <= right) { |
| 16 | // Avoid overflowing in the midpoint calculation |
| 17 | const mid = left + (right - left) / 2; |
| 18 | // Compare the midpoint element with the key |
| 19 | switch (compareFn(items[mid])) { |
| 20 | .eq => return mid, |
| 21 | .lt => left = mid + 1, |
| 22 | .gt => right = mid - 1, |
| 23 | } |
| 24 | } |
| 25 | |
| 26 | return null; |
| 27 | } |
| 28 | |
| 29 | test "std.sort.binarySearch" { |
| 30 | const S = struct { |
| 31 | fn makeComparisonPred(comptime T: type, value: T) type { |
| 32 | return struct { |
| 33 | fn pred(v: T) math.Order { |
| 34 | return math.order(v, value); |
| 35 | } |
| 36 | }; |
| 37 | } |
| 38 | }; |
| 39 | testing.expectEqual( |
| 40 | @as(?usize, null), |
| 41 | binarySearch(u32, &[_]u32{}, S.makeComparisonPred(u32, 1).pred), |
| 42 | ); |
| 43 | testing.expectEqual( |
| 44 | @as(?usize, 0), |
| 45 | binarySearch(u32, &[_]u32{1}, S.makeComparisonPred(u32, 1).pred), |
| 46 | ); |
| 47 | testing.expectEqual( |
| 48 | @as(?usize, null), |
| 49 | binarySearch(u32, &[_]u32{0}, S.makeComparisonPred(u32, 1).pred), |
| 50 | ); |
| 51 | testing.expectEqual( |
| 52 | @as(?usize, 4), |
| 53 | binarySearch(u32, &[_]u32{ 1, 2, 3, 4, 5 }, S.makeComparisonPred(u32, 5).pred), |
| 54 | ); |
| 55 | testing.expectEqual( |
| 56 | @as(?usize, 0), |
| 57 | binarySearch(u32, &[_]u32{ 2, 4, 8, 16, 32, 64 }, S.makeComparisonPred(u32, 2).pred), |
| 58 | ); |
| 59 | testing.expectEqual( |
| 60 | @as(?usize, 1), |
| 61 | binarySearch(i32, &[_]i32{ -7, -4, 0, 9, 10 }, S.makeComparisonPred(i32, -4).pred), |
| 62 | ); |
| 63 | testing.expectEqual( |
| 64 | @as(?usize, 3), |
| 65 | binarySearch(i32, &[_]i32{ -100, -25, 2, 98, 99, 100 }, S.makeComparisonPred(i32, 98).pred), |
| 66 | ); |
| 67 | } |
| 68 | |
| 8 | 69 | /// Stable in-place sort. O(n) best case, O(pow(n, 2)) worst case. O(1) memory (no allocator required). |
| 9 | 70 | pub fn insertionSort(comptime T: type, items: []T, lessThan: fn (lhs: T, rhs: T) bool) void { |
| 10 | 71 | var i: usize = 1; |
LemonBoy <thatlemon@gmail.com> 2020-01-31 00:40:43+01:00