leetcode

1287.cpp (476B)

 class Solution {
   public:
     int findSpecialInteger(vector<int> &arr) {
         const int n = size(arr), quarter = n / 4;
         for (const int candidate : {arr[n / 4], arr[n / 2], arr[3 * n / 4]}) {
             const int left = lower_bound(begin(arr), end(arr), candidate) - begin(arr);
             const int right = upper_bound(begin(arr), end(arr), candidate) - begin(arr);
             if (right - left > quarter) return candidate;
         }
         return -1;
     }
 };