原题链接:
https://leetcode.cn/problems/spiral-matrix/

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/**
    右下左上 
 */
class Solution {
    // 注意一下坐标就行了 程序中的坐标系会与传统理解坐标系有些不同
    public int [] dx = new int [] {0,1,0,-1};
    public int [] dy = new int [] {1,0,-1,0}; 
    public List<Integer> spiralOrder(int[][] matrix) {
        int m = matrix.length;
        int n = matrix[0].length;
        boolean [][] vis = new boolean [m][n];
        ArrayList<Integer> res = new ArrayList<>();

        int cur = 0;
        int x = 0, y = 0;
        int d = 0;
        while(cur != m * n){
            res.add(matrix[x][y]);
            vis[x][y] = true;
            cur++; 
            int tx = x + dx[d];
            int ty = y + dy[d];
            if( tx < 0 || ty <  0 ||  tx == m || ty == n || vis[tx][ty]){
                d = (d + 1) % 4;
                tx = x + dx[d];
                ty = y + dy[d];
            }
            x = tx;
            y = ty;
        }

        return res;
    }
}