Leetcode59 Spiral Matrix II

Posted 2022-12-01 xuweimdm

Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
] 

Solution1

public class Solution 
    public int[][] generateMatrix(int n) 
        int[][] result = new int[n][n];
        for(int i=0,k=1;i<(n+1)/2;i++)
            for(int j=i;j<n-i;j++) result[i][j] = k++;
            for(int j=i+1;j<n-i;j++) result[j][n-i-1] = k++;
            for(int j=n-i-2;j>=i;j--) result[n-i-1][j] = k++;
            for(int j=n-i-2;j>i;j--) result[j][i] = k++;
        
        return result;        
    

Solution2

public class Solution 
    public int[][] generateMatrix(int n) 
        int[][] result = new int[n][n];
        int left=0,right=n-1,top=0,down=n-1,k=1;
        for(;left<=right;left++)
            for(int i=left;i<=right;i++) result[top][i] = k++;
            for(int i=++top;i<=down;i++) result[i][right] = k++;
            for(int i=--right;i>=left;i--) result[down][i] = k++;
            for(int i=--down;i>=top;i--) result[i][left] = k++;

        
        return result;