1 files changed, 59 insertions, 0 deletions
diff --git a/util/mem.zig b/util/mem.zig
index 89ba67b..3b68dad 100644
--- a/util/mem.zig
+++ b/util/mem.zig
@@ -1,5 +1,7 @@
 const std = @import("std");
+
 const math = std.math;
+const testing_allocator = std.testing.allocator;
 
 /// Returns the position of the smallest number in a slice.
 pub fn min_idx(comptime T: type, slice: []const T) usize {
@@ -15,3 +17,60 @@ pub fn min_idx(comptime T: type, slice: []const T) usize {
     }
     return idx;
 }
+
+/// Returns a slice of the duplicated values amongst all slices.
+/// { {1,2,3,4}, {4,5,6,1} } -> {1,4}
+pub fn dupl_values(comptime T: type, allocator: std.mem.Allocator, haystacks: []const []const T) ![]T {
+    var haystacks_maps = blk: {
+        var r = std.ArrayList(std.AutoHashMap(T, bool)).init(allocator);
+        for (haystacks) |haystack| {
+            var haystack_map = std.AutoHashMap(T, bool).init(allocator);
+            for (haystack) |item| {
+                try haystack_map.put(item, true);
+            }
+            try r.append(haystack_map);
+        }
+        break :blk r.toOwnedSlice();
+    };
+
+    defer blk: {
+        for (haystacks_maps) |*haystack| {
+            haystack.deinit();
+        }
+        allocator.free(haystacks_maps);
+        break :blk;
+    }
+
+    var dupl = std.ArrayList(T).init(allocator);
+    var seen = std.AutoHashMap(T, bool).init(allocator);
+    defer seen.deinit();
+
+    for (haystacks[0]) |item| {
+        if (seen.contains(item))
+            continue;
+
+        try seen.put(item, true);
+
+        var duplicated = true;
+
+        for (haystacks_maps[1..]) |map| {
+            if (!map.contains(item)) {
+                duplicated = false;
+                continue;
+            }
+        }
+
+        if (duplicated)
+            try dupl.append(item);
+    }
+
+    return dupl.toOwnedSlice();
+}
+
+test "dupl_values" {
+    const haystack = [_][]const u8{ &[_]u8{ 1, 2, 3, 1 }, &[_]u8{ 2, 3, 1, 5 }, &[_]u8{ 3, 2, 1, 4 } };
+    var foo = try dupl_values(u8, testing_allocator, &haystack);
+    defer testing_allocator.free(foo);
+
+    try std.testing.expect(std.mem.eql(u8, foo, &[_]u8{ 1, 2, 3 }));
+}