【Leetcode】240. Search a 2D Matrix II（思维）-蒲公英云

【Leetcode】240. Search a 2D Matrix II（思维）

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.

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.

题目大意：

在一个二维数组中找出target。数组按照行列数组由大到小顺序排列。

解题思路：

如果当前（0，0）的数比tar小，我们需要从行的方面考虑从0到m-1，i++

当前的数比tar大，我们需要从列方面考虑从n-1到0，j—

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