Add util/bitops

Author: xirc

lib/cpalgo/util/bitops.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <functional>
+#include <stdexcept>
+
+// Iterates subsets of given bitset `S`.
+//
+// S = b0101
+// bs = { 0101, 0100, 0001, 0000 }
+//
+// Time: O(2**M)
+//   where M is the bit count of the given bitset
+//
+inline void iterate_subsets(
+    int S,
+    std::function<void(int)> const& f
+) {
+    if (S < 0) throw std::out_of_range("S");
+    for (auto bs = S; true; bs = (bs - 1) & S) {
+        f(bs);
+        if (bs == 0) break;
+    }
+}

lib/cpalgo/util/tests/bitops_test.cpp

@@ -0,0 +1,27 @@
+#include <bits/stdc++.h>
+#include "gtest/gtest.h"
+#include "cpalgo/util/bitops.hpp"
+
+using namespace std;
+
+TEST(BitOpsTest, IterateSubsets) {
+
+    int S = (1 << 0) | (1 << 2) | (1 << 3);
+    set<int> subsets;
+    iterate_subsets(S, [&](int bs) {
+        subsets.insert(bs);
+    });
+    set<int> expected_subsets = {
+        (1 << 0) | (1 << 2) | (1 << 3),
+        (1 << 2) | (1 << 3),
+        (1 << 0) | (1 << 3),
+        (1 << 3),
+        (1 << 0) | (1 << 2),
+        (1 << 2),
+        (1 << 0),
+        0
+    };
+
+    EXPECT_EQ(expected_subsets, subsets);
+
+}