LeetCode OJ 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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【题目分析】

与Spiral Matrix不同，这个题目要求生成一个方阵，方阵的值是螺旋递增的。

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【思路】

其实这个题目与上一个大同小异，他们遍历矩阵的顺序是相同的，只要把取值变为赋值就可以了。

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【java代码】

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];

        int top = 0;
        int bottom = n-1;
        int left = 0;
        int right = n-1;
        int num = 1;

        while(true){
            for(int i = left; i <= right; i++) matrix[top][i] = num++;
            top++;
            if(left > right || top > bottom) break;

            for(int i = top; i <= bottom; i++) matrix[i][right] = num++;
            right--;
            if(left > right || top > bottom) break;

            for(int i = right; i >= left; i--) matrix[bottom][i] = num++;
            bottom--;
            if(left > right || top > bottom) break;

            for(int i = bottom; i >= top; i--) matrix[i][left] = num++;
            left++;
            if(left > right || top > bottom) break;
        }

        return matrix;
    }
}