59-Spiral Matrix II

【题目】

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 ]
]

 

【分析】

1.与上一题的思路类似，按四个方向分别填充数组

【算法实现】

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] res=new int[n][n];
        int x1=0;
        int y1=0;
        int x2=n-1;
        int y2=n-1;
        int flag=1;
        while(x1<=x2&&y1<=y2) {
            for(int i=y1;i<=y2;i++)
                res[x1][i]=flag++;
            for(int i=x1+1;i<=x2;i++)
                res[i][y2]=flag++;
            if(x1!=x2)
                for(int i=y2-1;i>=y1;i--)
                    res[x2][i]=flag++;
            if(y1!=y2)
                for(int i=x2-1;i>x1;i--)
                    res[i][y1]=flag++;
            x1++;
            y1++;
            x2--;
            y2--;
        }
        return res;
    }
}