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std.mem: add indexOfMin and indexOfMax #9915

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merged 2 commits into from Jan 29, 2022
Merged

std.mem: add indexOfMin and indexOfMax #9915

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std.mem: Add functions to find the index of the mimimum/maximum value…
Oct 7, 2021
100b8a2
Add std.mem.minMax() and std.mem.IndexOfMinMax()
Oct 22, 2021
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100 changes: 98 additions & 2 deletions lib/std/mem.zig
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
Expand All @@ -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);
Expand All @@ -2165,7 +2169,99 @@ 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');
}

/// 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 {
assert(slice.len > 0);
var best = slice[0];
var index: usize = 0;
for (slice[1..]) |item, i| {
if (item < best) {
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The comparison predicate should be specified by the user to allow for extra flexibility and custom non-scalar types.

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I'm not sure about that. The precedent from std.math.min and std.mem.min is to only support scalar types. A custom predicate would be good to have, but maybe open an issue first?

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);
}

/// 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 {
Expand Down