378_py.txt

class Solution
{
public:
    int kthSmallest(vector<vector<int>>& m, int k) 
    {
        int left = m[0][0];
        int right = m.back().back();
        
        while(left < right )
            
        {
            int mid = left + (right - left) / 2;
            
            int count = lessthan(m,mid);
            
            if(count < k)
                left = mid + 1 ;
            
            else
                right = mid;
            
            
        }
        
        
        return left;
        
    }
    
    int lessthan(vector<vector<int>>& m, int target)
    {
        int i = m.size()-1, j = 0;
        int res = 0;
        
        while(i >= 0 && j < m.size())
        {
            if(m[i][j] <= target)
            {
                res += i+1; //该列以上行都小于target;
                
                j++ ;  // 扫描下一列；
                
                
                
            }
            
            else
                i-- ; //上一行
            
            
        }
        
        return res;
        
        
        
    }
};