search-a-2d-matrix（二维矩阵查找）

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, returntrue.

class Solution {
public:
    bool searchMatrix(vector<vector<int> > &matrix, int target) {
        int m = matrix.size();
        int n = matrix[0].size();
        int c = n-1;
        for(int r = 0;(r<m)&&(c>=0);)
        {
            if(matrix[r][c]>target)
            {
                c--;
            }
            else if(matrix[r][c]<target)
            {
                r++;
            }
            else
                return true;
        }
        return false;
    }
    //每次比较行末，由于已经排序好，可以进行行列删除
};