Leetcode107: 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.

从右上角开始比较，奇怪的是用for循环会报超时？

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;            }};