Data update

Task/Quickselect-algorithm/Zig/quickselect-algorithm.zig

@@ -0,0 +1,69 @@
+const std = @import("std");
+
+fn partition(comptime T: type, a: []T, left: usize, right: usize, pivot: usize) usize {
+    std.mem.swap(T, &a[pivot], &a[right]);
+    var store_index = left;
+    var i = left;
+    while (i < right) : (i += 1) {
+        if (a[i] < a[right]) {
+            std.mem.swap(T, &a[store_index], &a[i]);
+            store_index += 1;
+        }
+    }
+    std.mem.swap(T, &a[right], &a[store_index]);
+    return store_index;
+}
+
+fn pivotIndex(left: usize, right: usize) usize {
+    return left + (right - left) / 2;
+}
+
+fn select(comptime T: type, a: []T, left_init: usize, right_init: usize, n: usize) void {
+    var left = left_init;
+    var right = right_init;
+
+    while (true) {
+        if (left == right) {
+            break;
+        }
+
+        var pivot = pivotIndex(left, right);
+        pivot = partition(T, a, left, right, pivot);
+
+        if (n == pivot) {
+            break;
+        } else if (n < pivot) {
+            right = pivot - 1;
+        } else {
+            left = pivot + 1;
+        }
+    }
+}
+
+// Rearranges the elements of 'a' such that the element at index 'n' is
+// the same as it would be if the array were sorted, smaller elements are
+// to the left of it and larger elements are to its right.
+fn nthElement(comptime T: type, a: []T, n: usize) void {
+    select(T, a, 0, a.len - 1, n);
+}
+
+pub fn main() !void {
+    const allocator = std.heap.page_allocator;
+    const a = [_]i32{ 9, 8, 7, 6, 5, 0, 1, 2, 3, 4 };
+
+    var n: usize = 0;
+    while (n < a.len) : (n += 1) {
+        var b = try allocator.alloc(i32, a.len);
+        defer allocator.free(b);
+
+        // Copy elements one by one instead of using mem.copy
+        for (0..a.len) |i| {
+            b[i] = a[i];
+        }
+
+        nthElement(i32, b, n);
+
+        const stdout = std.io.getStdOut().writer();
+        try stdout.print("n = {}, nth element = {}\n", .{ n + 1, b[n] });
+    }
+}