Search a 2D Matrix IIWrite an efficient algorithm that searches for a value in an m x n matrix. This

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

.
在这道题中，由于矩阵的行和列已经分别排序好了，所以可以利用分治算法，将矩阵分为行和列分开比较，先比较每一列最后一个数与查找目标的大小，
如果比目标数小，则比较下一列最后一行的数和目标数的大小；如果比目标数大，则比较该数同一列上一行的数，逐次向上，一旦找到目标数，即返回

true，否则返回false。

bool searchMatrix(vector<vector<int>>& matrix, int target) {

int row = matrix.size();
if(row == 0) return false;
int column = matrix[0].size();
int x = row - 1;
int y = 0;
while(x >= 0 && y < m)
{

if(matrix[y][x] == target) return true;
else if(matrix[y][x] > target)
{
x--;
}
else y++;
} 
return false;

}