leetcode 240 查询一个排序好的矩阵中是否存在target

首先题目如下所示：

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.

解题思路：从右上角开始往左下角找寻答案，如果大了就j–，如果小了就i++，这样子可以完全遍历矩阵，最后实现时间65ms，还可以了

class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
int m =matrix.size();
if(m==0) return false;
int n = matrix[0].size();
int i =0,j=n-1;
while(i<m && j>=0){
if(matrix[i][j] == target) return true;
else if(matrix[i][j] > target)
j--;
else
i++;
}
return false;
}
};