Search a 2D Matrix II

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 in ascending from left to right.
Integers in each column are sorted in ascending from top to bottom.
For example,

Consider the following matrix:

[
[1, 4, 7, 11, 15],
[2, 5, 8, 12, 19],
[3, 6, 9, 16, 22],
[10, 13, 14, 17, 24],
[18, 21, 23, 26, 30]
]
Given target = 5, return true.

Given target = 20, return false.

分析：用两个变量x,y来记录位置，根据排序好的序列，贪心即可

代码如下：

bool searchMatrix(vector<vector<int> >& matrix, int target) {        int xbegin=0;        int ybegin=0;        int m=matrix.size();        if(m==0) return 0;        int n=matrix[0].size();        int x=0;        int y=n-1;        if(n==0) return 0;        while(x<m&&y>=0){            if(matrix[x][y]==target) return 1;            if(matrix[x][y]<target) {            x++;        }        else        y--;        }        return 0;    }