Create count-number-of-bad-pairs.cpp

Author: kamyu104

C++/count-number-of-bad-pairs.cpp

@@ -0,0 +1,15 @@
+// Time:  O(n)
+// Space: O(n)
+
+// freq table
+class Solution {
+public:
+    long long countBadPairs(vector<int>& nums) {
+        int64_t result = size(nums) * (size(nums) - 1) / 2;
+        unordered_map<int, int> cnt;
+        for (int i = 0; i < size(nums); ++i) {
+            result -= cnt[nums[i] - i]++;
+        }
+        return result;
+    }
+};