59. Spiral Matrix II

Question

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

Solution

用数字表示方向，根据方向决定坐标移动的方式。

当方向改变时，减少对应的边界。

Code

class Solution {
    public int[][] generateMatrix(int n) {
        int dir = 0;
        int p = 0, q = 0;
        int right = n-1, down = n-1;
        int left = 0, up = 0;
        int count = 0;
        int[][] ret = new int[n][n];
        for(int i = 0; i < n; i++){
            for(int j = 0; j < n; j++){
                switch(dir){
                    case 0:
                        count++;
                        ret[p][q] = count;
                        q++;
                        if(q == right){
                            up++;
                            dir = 1;
                        }
                        break;
                    case 1:
                        count++;
                        ret[p][q] = count;
                        p++;
                        if(p == down){
                            right--;
                            dir = 2;
                        }
                        break;
                    case 2:
                        count++;
                        ret[p][q] = count;
                        q--;
                        if(q == left){
                            down--;
                            dir = 3;
                        }
                        break;
                    case 3:
                        count++;
                        ret[p][q] = count;
                        p--;
                        if(p == up){
                            left++;
                            dir = 0;
                        }
                    break;
                }
            }
        }
        return ret;
    }
}