题目描述：

Write an efficient algorithm that searches for a value in an m 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, return true.

代码：

bool searchMatrix(vector<vector<int> > &matrix, int target, int left, int right ,int length)
{
        if(left > right)
            return false;
        int mid = (left + right)/2;
        if(target == matrix[mid / length][mid % length])
            return true;
        else if(target > matrix[mid / length][mid % length])
            return searchMatrix(matrix,target,mid+1,right,length);
        else
            return searchMatrix(matrix,target,left,mid-1,length);
}

bool searchMatrix(vector<vector<int> > &matrix, int target)
{
    return searchMatrix(matrix,target,0,matrix.size()*matrix[0].size()-1,matrix[0].size());
}

LeetCode:Search a 2D Matrix