Add C++ solution of problem #2364

Author: Cuda-Chen

2364/solution.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+    long long countBadPairs(vector<int>& A) {
+        unordered_map<int, vector<int>> m; // {A[i] - i, {idxs}}
+        int n = A.size();
+
+        // preserve the monotonicaliation of index of pairs
+        for(int i = 0; i < n; i++)
+            m[A[i] - i].push_back(i);
+
+        long long ans = 0LL;
+        for(auto &[_, v] : m) {
+            int sz = v.size();
+            for(int i = 0; i < sz; i++) {
+                int idx = v[i];
+                int expected = (n - idx - 1); // expected pairs or current index
+                int good = (sz - i - 1); // the "good" pairs, i.e., i < j and j - i == A[j] - A[i]
+
+                ans += (expected - good); // get # the "bad" pairs
+            }
+        }
+        return ans;
+    }
+};