LeetCode - Refresh - Search a 2D Matrix

 1 class Solution {
 2 public:
 3     bool searchMatrix(vector<vector<int> > &matrix, int target) {
 4         if (matrix.size() == 0) return false;
 5         int n = matrix.size(), m = matrix[0].size(), start = 0, end = n*m-1, mid = 0;
 6         while (start <= end) {
 7             mid = (start + end)/2;
 8             if (matrix[mid/m][mid%m] == target) return true;
 9             if (matrix[mid/m][mid%m] > target) end = mid-1;
10             else start = mid+1;
11         }
12         return false;
13     }
14 };