[leetcode] 240. Search a 2D Matrix II

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

.

解法一：

从左下角数字开始，--row都比他小，++col都比他大。

class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
if(matrix.empty()||matrix[0].empty()) return false;
if(target < matrix[0][0] || target > matrix.back().back()) return false;

int row = matrix.size()-1;
int col = 0;
while(1){
if(matrix[row][col]<target) ++col;
else if (matrix[row][col]>target) --row;
else return true;

if(row<0 || col>=matrix[0].size()) break;
}
return false;

}
};