先列二分法，再行二分法

    1. class Solution {
    2. public:
    3.     bool searchMatrix(vector<vector<int>>& matrix, int target) {
    4.         if(!matrix.size() || !matrix[0].size()) return false;
    5.         int rmin = 0, rmax = matrix.size() - 1;
    6.         while(rmin < rmax)
    7.         {
    8.             int mid = (rmin + rmax + 1) >> 1;
    9.             if(target < matrix[mid][0])
    10.                 rmax = mid - 1;
    11.             else
    12.                 rmin = mid;
    13.         }
    14.         // cout << "rmin: "<< rmin << endl;
    15.         if(target < matrix[rmin][0]) return false;
    16.         int cmin = 0, cmax = matrix[0].size() - 1;
    17.         while(cmin < cmax)
    18.         {
    19.             int mid = (cmin + cmax) >> 1;
    20.             // cout << "cmin & cmax & mid: " << cmin << " " << cmax << " " << mid << endl;
    21.             if(matrix[rmin][mid] < target)
    22.                 cmin = mid + 1;
    23.             else 
    24.                 cmax = mid;
    25.         }
    26.         // cout << "cmax: " << cmax << endl;
    27.         if(matrix[rmin][cmin] != target) return false;
    28.         return true;
    29.     }
    30. };