问题描述：

Write an efficient algorithm that searches for a value in anm x n matrix. This matrix has the following properties:

• Integers in each row are sorted from left to right.
• The first integer of each row is greater than the last integer of the previous row.

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, returntrue.

基本思路：

二分查找。

代码：

    bool searchMatrix(vector<vector<int> > &matrix, int target) {  //C++
        int rows = matrix.size();
        if(rows == 0)
            return false;
        int cols = matrix[0].size();
        
        int low = 0, high = rows*cols-1;
        int i,j;
        while(low <= high)
        {
            int mid = (low + high)/2;
            i  = mid/cols;
            j = mid%cols;
            
            if(matrix[i][j] == target)
                return true;
            if(matrix[i][j] < target)
                low = mid +1;
            else high = mid -1;
            
                
        }
        return false;
    }

[leetcode]Search a 2D Matrix