feat(LeetCode): Solve leetcode/leetcoding_challenge/2025/apr2025/week3/count_the_number_of_fair_pairs.cpp

Author: htbkoo

src/onlinePlatform/leetcode/leetcoding_challenge/2025/apr2025/week3/count_the_number_of_fair_pairs.cpp

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+#include <algorithm>
+#include <vector>
+#include <queue>
+#include <set>
+#include <limits>
+#include <map>
+#include <unordered_set>
+#include <unordered_map>
+#include <iterator>
+#include <sstream>
+#include <iostream> // includes cin to read from stdin and cout to write to stdout
+using namespace std; // since cin and cout are both in namespace std, this saves some text
+
+class Solution {
+public:
+    long long countFairPairs(vector<int>& nums, int lower, int upper) {
+        sort(begin(nums), end(nums));
+        
+        long long answer = 0;
+        for (int i = 0; i < nums.size(); ++i) {
+            auto num = nums[i];
+            
+            int left = max(i + 1, (int) distance(begin(nums), lower_bound(begin(nums), end(nums), lower - num)));
+            int right = distance(begin(nums),upper_bound(begin(nums), end(nums), upper - num));
+            
+            answer += max(0, right - left);
+        }
+        
+        return answer;
+    }
+};
+
+int main() {
+    Solution soln;
+    vector nums{0,0,0,0,0,0};
+    cout << soln.countFairPairs(nums, 0 , 0) << endl;
+    return 0;
+}