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.

剑指OFFER的题目，从右上角查找即可，时间复杂度为O(N)。

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