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

For example,
Given n = 3, 

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

思路

这道题其实没有什么算法上的技术含量。题目需要我们按照蛇形的路线生成一个数组，我们其实可以按照题目的要求，碰到不合适的路径不走即可。比较考验编程能力的就是在边界条件和实现的过程中的技巧。

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public class Solution {
    public int[][] generateMatrix(int n) {
        // A very good way to assign dynamic-length array
        int[][] ans = new int[n][];
        for (int i = 0; i < n; i++){
            ans[i] = new int[n];
            for (int j = 0; j < n; j++){
                ans[i][j] = 0;
            }
        }
        int x = 0;
        int y = 0;
        boolean right = true;
        boolean down = false;
        boolean up = false;
        boolean left = false;
        for (int count = 1; count <= n * n; count++){
            ans[x][y] = count;
            boolean rightblock = y + 1 >= n || ans[x][y+1] > 0;
            boolean leftblock = y - 1 < 0 || ans[x][y-1] > 0;
            boolean upblock = x - 1 < 0 || ans[x-1][y] > 0;
            boolean downblock = x + 1 >= n || ans[x+1][y] > 0;
            if(rightblock && leftblock && upblock){
                right = up = left = false;
                down = true;
            }
            else if(rightblock && leftblock && downblock){
                right = down = left = false;
                up = true;
            }
            else if(rightblock && downblock && upblock){
                right = down = up = false;
                left = true;
            }
            else if(leftblock && downblock && upblock){
                left = down = up = false;
                right = true;
            }
            if(left){
                y--;
            }
            else if(right){
                y++;
            }
            else if(down){
                x++;
            }
            else if(up){
                x--;
            }
        }
        return ans;
    }
}