From dddbd2f511f505ad4018ba007f065ea2b4ec8f79 Mon Sep 17 00:00:00 2001
From: Mikhail Popov <mpopov@fastmail.fm>
Date: Fri, 8 Oct 2021 00:37:50 +0200
Subject: [PATCH] std.mem: Add functions to find the index of the
 mimimum/maximum value in a slice.

---
 lib/std/mem.zig | 52 +++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/lib/std/mem.zig b/lib/std/mem.zig
index 5c0e3b30b7..a69d1dcda0 100644
--- a/lib/std/mem.zig
+++ b/lib/std/mem.zig
@@ -2143,6 +2143,7 @@ fn testWriteIntImpl() !void {
 /// Returns the smallest number in a slice. O(n).
 /// `slice` must not be empty.
 pub fn min(comptime T: type, slice: []const T) T {
+    assert(slice.len > 0);
     var best = slice[0];
     for (slice[1..]) |item| {
         best = math.min(best, item);
@@ -2151,12 +2152,15 @@ pub fn min(comptime T: type, slice: []const T) T {
 }
 
 test "mem.min" {
-    try testing.expect(min(u8, "abcdefg") == 'a');
+    try testing.expectEqual(min(u8, "abcdefg"), 'a');
+    try testing.expectEqual(min(u8, "bcdefga"), 'a');
+    try testing.expectEqual(min(u8, "a"), 'a');
 }
 
 /// Returns the largest number in a slice. O(n).
 /// `slice` must not be empty.
 pub fn max(comptime T: type, slice: []const T) T {
+    assert(slice.len > 0);
     var best = slice[0];
     for (slice[1..]) |item| {
         best = math.max(best, item);
@@ -2165,7 +2169,51 @@ pub fn max(comptime T: type, slice: []const T) T {
 }
 
 test "mem.max" {
-    try testing.expect(max(u8, "abcdefg") == 'g');
+    try testing.expectEqual(max(u8, "abcdefg"), 'g');
+    try testing.expectEqual(max(u8, "gabcdef"), 'g');
+    try testing.expectEqual(max(u8, "g"), 'g');
+}
+
+/// 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 {
+    assert(slice.len > 0);
+    var best = slice[0];
+    var index: usize = 0;
+    for (slice[1..]) |item, i| {
+        if (item < best) {
+            best = item;
+            index = i + 1;
+        }
+    }
+    return index;
+}
+
+test "mem.indexOfMin" {
+    try testing.expectEqual(indexOfMin(u8, "abcdefg"), 0);
+    try testing.expectEqual(indexOfMin(u8, "bcdefga"), 6);
+    try testing.expectEqual(indexOfMin(u8, "a"), 0);
+}
+
+/// Returns the index of the largest number in a slice. O(n).
+/// `slice` must not be empty.
+pub fn indexOfMax(comptime T: type, slice: []const T) usize {
+    assert(slice.len > 0);
+    var best = slice[0];
+    var index: usize = 0;
+    for (slice[1..]) |item, i| {
+        if (item > best) {
+            best = item;
+            index = i + 1;
+        }
+    }
+    return index;
+}
+
+test "mem.indexOfMax" {
+    try testing.expectEqual(indexOfMax(u8, "abcdefg"), 6);
+    try testing.expectEqual(indexOfMax(u8, "gabcdef"), 0);
+    try testing.expectEqual(indexOfMax(u8, "a"), 0);
 }
 
 pub fn swap(comptime T: type, a: *T, b: *T) void {