Create count-triplets-with-even-xor-set-bits-ii.cpp

Author: kamyu104

C++/count-triplets-with-even-xor-set-bits-ii.cpp

@@ -0,0 +1,44 @@
+// Time:  O(nlogr), r = max(max(a), max(b), max(c))
+// Space: O(1)
+
+// bit manipulation, parity
+class Solution {
+public:
+    long long tripletCount(vector<int>& a, vector<int>& b, vector<int>& c) {
+        const auto& count = [](const auto& a) {
+            const auto& odd = accumulate(cbegin(a), cend(a), 0, [](const auto& total, const auto& x) {
+                return total + (__builtin_popcount(x) & 1);
+            });
+            return vector<int64_t>{static_cast<int>(size(a)) - odd, odd};
+        };
+
+        vector<vector<int64_t>> cnt = {count(a), count(b), count(c)};
+        int64_t result = 0;
+        for (int i = 0; i < 4; ++i) {
+            result += cnt[0][i == 0 || i == 1 ? 0 : 1] * 
+                      cnt[1][i == 0 || i == 2 ? 0 : 1] *
+                      cnt[2][i == 0 || i == 3 ? 0 : 1];
+        }
+        return result;
+    }
+};
+
+// Time:  O(nlogr), r = max(max(a), max(b), max(c))
+// Space: O(1)
+// bit manipulation, parity
+class Solution2 {
+public:
+    long long tripletCount(vector<int>& a, vector<int>& b, vector<int>& c) {
+        const auto& count = [](const auto& a) {
+            const auto& odd = accumulate(cbegin(a), cend(a), 0, [](const auto& total, const auto& x) {
+                return total + (__builtin_popcount(x) & 1);
+            });
+            return pair<int64_t, int64_t>(static_cast<int>(size(a)) - odd, odd);
+        };
+
+        const auto& [even1, odd1] = count(a);
+        const auto& [even2, odd2] = count(b);
+        const auto& [even3, odd3] = count(c);
+        return even1 * even2 * even3 + even1 * odd2 * odd3 + odd1 * even2 * odd3 + odd1 * odd2 * even3;
+    }
+};