题目

输入一个矩阵，按照从外向里以顺时针的顺序依次打印出每一个数字。

数据范围

矩阵中元素数量 [0,400][0,400]。

样例

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

输出：[1,2,3,4,8,12,11,10,9,5,6,7]

解析

直接模拟，遇到边界或已经遍历过的元素时，就顺时针改变方向

代码

Python

class Solution(object):
    def printMatrix(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[int]
        """
        ans = []
        if len(matrix) == 0 or len(matrix[0]) == 0:
            return ans
        n, m = len(matrix), len(matrix[0])
            
        dx = [-1, 0, 1, 0]
        dy = [0, 1, 0, -1]
        st = [[False for _ in range(m)] for _ in range(n)]
        x = 0
        y = 0
        d = 1
        for i in range(n * m):
            ans.append(matrix[x][y])
            st[x][y] = True
            a = x + dx[d]
            b = y + dy[d]
            if a < 0 or a >= n or b < 0 or b >= m or st[a][b]:
                d = (d + 1) % 4
                a = x + dx[d]
                b = y + dy[d]
            x = a
            y = b
            # for i in range(len(st)):
            #     print(st[i])
            # print()
        return ans
        

GO

func printMatrix(matrix [][]int) []int {
    ans := []int{}
    if len(matrix) == 0 || len(matrix[0]) == 0 {
        return ans
    }
    
    n, m := len(matrix), len(matrix[0])
    st := make([][]bool, n)
    for i := 0; i < n; i ++ {
        st[i] = make([]bool, m)
    }
    dx, dy := []int{-1, 0, 1, 0}, []int{0, 1, 0, -1}
    x, y, d := 0, 0, 1
    for k := 0; k < n * m; k ++ {
        ans = append(ans, matrix[x][y])
        st[x][y] = true
        a, b := x + dx[d], y + dy[d]
        if a < 0 || a >= n || b < 0 || b >= m || st[a][b] {
            d = (d + 1) % 4;
            a, b = x + dx[d], y + dy[d]
        }
        x, y = a, b
    }
    return ans
}