Add Fisher-Yates/Knuth shuffling algorithm

Zig/src/math/prob/fisher_yates.zig

@@ -0,0 +1,40 @@
+const std = @import("std");
+const rand = std.rand;
+
+const Allocator = std.mem.Allocator;
+const swap = std.mem.swap;
+
+/// Shuffle slice in place with Fisher-Yates/Knuth.
+pub fn shuffle_in_place(comptime T: type, slice: []T, seed: u64) void {
+    var prng = rand.DefaultPrng.init(seed);
+    const random = prng.random();
+
+    var i: usize = undefined;
+    if (@subWithOverflow(usize, slice.len, 1, &i)) {
+        // Empty slice. Nothing to shuffle.
+        i = 0;
+    }
+
+    // https://en.wikipedia.org/wiki/Fisher%E2%80%93Yates_shuffle#The_modern_algorithm
+    while (i > 0) {
+        const j = random.uintAtMost(usize, i);
+        swap(T, &slice[i], &slice[j]);
+
+        i -= 1;
+    }
+}
+
+pub fn shuffle_copy(
+    comptime T: type,
+    allocator: Allocator,
+    slice: []T,
+    seed: u64,
+) ![]T {
+    // Copy slice to new memory to avoid mutating the original
+    var shuffled = try allocator.alloc(T, slice.len);
+    std.mem.copy(T, shuffled, slice);
+
+    shuffle_in_place(T, shuffled, seed);
+
+    return shuffled;
+}