leetcode_contest56

class  {
public:
    int f_abs(int x){
        return x > 0 ? x : -x;
    }
    int count(vector<int>& nums, int mid){
        int cnt = 0;
        int n = nums.size();
        int j = 0;
        
        for(int i = 0; i < n; i++){
            while(j < i && (nums[i] - nums[j]) > mid) j++;
            cnt += (i - j);
        }
        return cnt;
    }
    int smallestDistancePair(vector<int>& nums, int k) {
        int n = nums.size();
        sort(nums.begin(),nums.end());
        int left = 0;
        int right = nums[n-1] - nums[0];
        //二分，若小于差值mid的个数小于k，则需要将差值增大，反之，则减小。
        while(left < right){
            int mid = (right + left) / 2;
            if(count(nums, mid) < k){
                left = mid + 1;
            }else{
                right = mid;
            }
        }
        return left;
    }
};