順時針列印矩陣

1. 題目描述

輸入一個矩陣，按照從外向裡以順時針的順序依次打印出每一個數字

2. 示例

[[ 1, 2, 3, 4],

[ 5, 6, 7, 8],

[ 9, 10, 11, 12],

[13, 14, 15, 16]]

則依次打印出數字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

3. 解題思路

順時針走，即向右->向下->向左->向上，一共要走（長*寬）步。

遇到邊界就改變方向，當向上碰到頂的時候，四個邊界都縮小。思路簡單，一個迴圈即可！

4. Java實現

import java.util.ArrayList;
public class Solution {
    public ArrayList<Integer> printMatrix(int [][] matrix) {
        ArrayList<Integer> res = new ArrayList();
        int rows = matrix.length;  // 行的大小
        int cols = matrix[0].length; // 列的大小
        
        if (rows == 0 || cols == 0){
            return res;
        }
        
        // 從左到右開始遍歷，right最右邊【列】，從上到下，bottom最底部【行】
        int left = 0, right = cols-1, top = 0, bottom = rows -1;
        
        while(left <= right && top <= bottom){
            // 從左到右開始遍歷
            for(int i = left; i <= right; i++){
                res.add(matrix[top][i]);
            }
            // 從上到下開始遍歷
            for (int i = top+1; i <= bottom; i++){
                res.add(matrix[i][right]);
            }
            // 從下往上開始遍歷
            if (top != bottom){
                for (int i = right-1; i>= left; i--){
                    res.add(matrix[bottom][i]);
                }
            }
            //從 右往左開始遍歷
            if (left != right){
                for (int i = bottom-1; i > top; i--){
                    res.add(matrix[i][left]);
                }
            }
            left++;
            right--;
            top++;
            bottom--;
        }
      return res;
    }
    
}
 

5. Python實現

# -*- coding:utf-8 -*-
class Solution:
    # matrix型別為二維列表，需要返回列表
    def printMatrix(self, matrix):
        if matrix == None:
            return
        rows = len(matrix)
        columns = len(matrix[0])
        start = 0
        while rows > start * 2 and columns > start * 2:
            self.PrintMatrixInCircle(matrix, columns, rows, start)
            start += 1
        print('')
 
    def PrintMatrixInCircle(self, matrix, columns, rows, start):
        endX = columns - 1 - start
        endY = rows - 1 - start
 
        # 從左到右列印一行
        for i in range(start, endX+1):
            number = matrix[start][i]
            print(number, ' ', end='')
 
        # 從上到下列印一行
        if start < endY:
            for i in range(start+1, endY+1):
                number = matrix[i][endX]
                print(number, ' ', end='')
 
        # 從右到左列印一行
        if start < endX and start < endY:
            for i in range(endX-1, start-1, -1):
                number = matrix[endY][i]
                print(number, ' ', end='')
 
        # 從下到上列印一行
        if start < endX and start < endY-1:
            for i in range(endY-1, start, -1):
                number = matrix[i][start]
                print(number, ' ', end='')
 

如果您覺得本文有用，請點個“在看”