LeetCode 59. 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 ]]
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给你一个数n生成一个包含1-n^2的螺旋形矩阵
样例
n = 3
矩阵为
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]

solution

相比问题一更简单，运用同样的规则遍历即可

public class Solution {
    public int[][] generateMatrix(int n) {
        if(n<0)
            return null;
        int[][] res = new int[n][n];
        
        int count = 1;
        
        int rowBegin = 0;
        int rowEnd = n-1;
        int colBegin = 0;
        int colEnd = n-1;
        
        while(rowBegin <= rowEnd && colBegin <= colEnd) {
            for(int i=colBegin;i<=colEnd;i++)
                res[rowBegin][i] = count++;
            rowBegin++;
            
            for(int i=rowBegin;i<=rowEnd;i++)
                res[i][colEnd] = count++;
            colEnd--;
            
            if(rowBegin <= rowEnd) {
                for(int i=colEnd;i>=colBegin;i--)
                    res[rowEnd][i] = count++;
                rowEnd--;
            }
            
            if(colBegin <= colEnd) {
                for(int i=rowEnd;i>=rowBegin;i--)
                    res[i][colBegin] = count++;
                colBegin++;
            }
        }
        return res;
    }
}