240. Search a 2D Matrix II

题目

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.

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思路

从右上角元素开始查

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代码

class Solution {public:    bool searchMatrix(vector<vector<int>>& matrix, int target) {        //从右上角开始查找        int row = matrix.size();        if(row == 0)        {            return false;        }        int col = matrix[0].size();        int checkNum;        int i = 0;        int j = col-1;        while(i < row && j >= 0)        {            checkNum = matrix[i][j];            if(checkNum == target)            {                return true;            }            if(checkNum > target)            {                j--;            }            else            {                i++;            }        }        return false;    }};