Spiral Matrix

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

Example 1:

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

Example 2:

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

分析

上下左右同时来，最后上下左右相碰就结束。 注意判断res.size<size 不是 ==！！！

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
         List<Integer> res = new ArrayList<>();
        if(matrix == null || matrix.length == 0)
            return res;
        
        int n = matrix.length,m = matrix[0].length;
        int sr = 0, er = matrix.length-1, sc = 0, ec = matrix[0].length-1;
        int size = n*m;
        while(er >=sr && ec>=sc){ //相交即可 不可越界
            for(int i = sc; i <= ec && res.size() < size; i ++){ //注意这里要判断res.size<size!!!!!
                res.add(matrix[sr][i]);
            }
            sr ++;
            for(int i = sr; i <= er&& res.size() < size; i ++){
                res.add(matrix[i][ec]);
            }
            ec -- ;
            for(int i = ec; i >=sc&& res.size() < size; i --){
                res.add(matrix[er][i]);
            }
            er --;
            for(int i = er; i >=sr&& res.size() < size; i --){
                res.add(matrix[i][sc]);
            }
            sc ++;
            
        }
        return res;
    }
}