From 100b8a244cdbcd16669e6b81ab82d6a628559e22 Mon Sep 17 00:00:00 2001
From: Mikhail Popov <mpopov@fastmail.fm>
Date: Fri, 22 Oct 2021 14:38:08 +0200
Subject: [PATCH] Add std.mem.minMax() and std.mem.IndexOfMinMax()

For finding the minimum and maximum values (and indices)
in a slice in a single pass.
---
 lib/std/mem.zig | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 48 insertions(+)

diff --git a/lib/std/mem.zig b/lib/std/mem.zig
index a69d1dcda0..6d5ae952eb 100644
--- a/lib/std/mem.zig
+++ b/lib/std/mem.zig
@@ -2174,6 +2174,26 @@ test "mem.max" {
     try testing.expectEqual(max(u8, "g"), 'g');
 }
 
+/// Finds the smallest and largest number in a slice. O(n).
+/// Returns an anonymous struct with the fields `min` and `max`.
+/// `slice` must not be empty.
+pub fn minMax(comptime T: type, slice: []const T) struct { min: T, max: T } {
+    assert(slice.len > 0);
+    var minVal = slice[0];
+    var maxVal = slice[0];
+    for (slice[1..]) |item| {
+        minVal = math.min(minVal, item);
+        maxVal = math.max(maxVal, item);
+    }
+    return .{ .min = minVal, .max = maxVal };
+}
+
+test "mem.minMax" {
+    try testing.expectEqual(minMax(u8, "abcdefg"), .{ .min = 'a', .max = 'g' });
+    try testing.expectEqual(minMax(u8, "bcdefga"), .{ .min = 'a', .max = 'g' });
+    try testing.expectEqual(minMax(u8, "a"), .{ .min = 'a', .max = 'a' });
+}
+
 /// Returns the index of the smallest number in a slice. O(n).
 /// `slice` must not be empty.
 pub fn indexOfMin(comptime T: type, slice: []const T) usize {
@@ -2216,6 +2236,34 @@ test "mem.indexOfMax" {
     try testing.expectEqual(indexOfMax(u8, "a"), 0);
 }
 
+/// Finds the indices of the smallest and largest number in a slice. O(n).
+/// Returns an anonymous struct with the fields `index_min` and `index_max`.
+/// `slice` must not be empty.
+pub fn indexOfMinMax(comptime T: type, slice: []const T) struct { index_min: usize, index_max: usize } {
+    assert(slice.len > 0);
+    var minVal = slice[0];
+    var maxVal = slice[0];
+    var minIdx: usize = 0;
+    var maxIdx: usize = 0;
+    for (slice[1..]) |item, i| {
+        if (item < minVal) {
+            minVal = item;
+            minIdx = i + 1;
+        }
+        if (item > maxVal) {
+            maxVal = item;
+            maxIdx = i + 1;
+        }
+    }
+    return .{ .index_min = minIdx, .index_max = maxIdx };
+}
+
+test "mem.indexOfMinMax" {
+    try testing.expectEqual(indexOfMinMax(u8, "abcdefg"), .{ .index_min = 0, .index_max = 6 });
+    try testing.expectEqual(indexOfMinMax(u8, "gabcdef"), .{ .index_min = 1, .index_max = 0 });
+    try testing.expectEqual(indexOfMinMax(u8, "a"), .{ .index_min = 0, .index_max = 0 });
+}
+
 pub fn swap(comptime T: type, a: *T, b: *T) void {
     const tmp = a.*;
     a.* = b.*;