leetcode 240. Search a 2D Matrix II 矩阵搜索 + 右上角搜索

刺骨的言语ヽ痛彻心扉 2022-06-08 12:46 120阅读 0赞

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.

对于排序好的矩阵，右上角开始搜索。

这道题很棒。

建议和[leetcode 378. Kth Smallest Element in a Sorted Matrix][] 和 [leetcode 668. Kth Smallest Number in Multiplication Table 有序矩阵搜索][leetcode 668. Kth Smallest Number in Multiplication Table]

代码如下：

/*
     * 右上角搜索
     * */
    class Solution 
    {
        public boolean searchMatrix(int[][] matrix, int target) 
        {
            if(matrix==null || matrix.length<=0)
                return false;
    
            int i=0 , j=matrix[0].length-1;
            while(i<matrix.length && j>=0)
            {
                if(matrix[i][j]==target)
                    return true;
                else if(matrix[i][j]>target)
                    j--;
                else 
                    i++;
            }
            return false;
        }
    }

下面是C++的做法，就是一个右上角搜索的做法，很经典

代码如下：

#include <iostream>
    #include <alogrithm>
    #include <set>
    #include <map>
    #include <vector>
    #include <stack>
    #include <queue>
    
    using namespace std;
    
    class Solution 
    {
    public:
        bool searchMatrix(vector<vector<int>>& mat, int target) 
        {
            if (mat.size() <= 0)
                return false;
            int i = 0;
            int j = mat[0].size() - 1;
            while (i < mat.size() && j >= 0)
            {
                if (mat[i][j] == target)
                    return true;
                else if (target < mat[i][j])
                    j--;
                else
                    i++;
            }
            return false;
        }
    };

[leetcode 378. Kth Smallest Element in a Sorted Matrix]: http://blog.csdn.net/jackzhang_123/article/details/78174215
[leetcode 668. Kth Smallest Number in Multiplication Table]: http://blog.csdn.net/jackzhang_123/article/details/78871859