一周刷完剑指offer-19-顺时针打印矩阵

顺时针打印矩阵

1. 题目描述

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

2. 示例

[[ 1, 2, 3, 4],

[ 5, 6, 7, 8],

[ 9, 10, 11, 12],

[13, 14, 15, 16]]

则依次打印出数字1,2,3,4,8,12,16,15,14,13,9,5,6,7,11,10.

3. 解题思路

顺时针走，即向右->向下->向左->向上，一共要走（长*宽）步。

遇到边界就改变方向，当向上碰到顶的时候，四个边界都缩小。思路简单，一个循环即可！

4. Java实现

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;
        }
        
        // 从左到右开始遍历，right最右边【列】，从上到下，bottom最底部【行】
        int left = 0, right = cols-1, top = 0, bottom = rows -1;
        
        while(left <= right && top <= bottom){
            // 从左到右开始遍历
            for(int i = left; i <= right; i++){
                res.add(matrix[top][i]);
            }
            // 从上到下开始遍历
            for (int i = top+1; i <= bottom; i++){
                res.add(matrix[i][right]);
            }
            // 从下往上开始遍历
            if (top != bottom){
                for (int i = right-1; i>= left; i--){
                    res.add(matrix[bottom][i]);
                }
            }
            //从 右往左开始遍历
            if (left != right){
                for (int i = bottom-1; i > top; i--){
                    res.add(matrix[i][left]);
                }
            }
            left++;
            right--;
            top++;
            bottom--;
        }
      return res;
    }
    
}

5. Python实现

# -*- coding:utf-8 -*-
class Solution:
    # matrix类型为二维列表，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
 
        # 从左到右打印一行
        for i in range(start, endX+1):
            number = matrix[start][i]
            print(number, ' ', end='')
 
        # 从上到下打印一行
        if start < endY:
            for i in range(start+1, endY+1):
                number = matrix[i][endX]
                print(number, ' ', end='')
 
        # 从右到左打印一行
        if start < endX and start < endY:
            for i in range(endX-1, start-1, -1):
                number = matrix[endY][i]
                print(number, ' ', end='')
 
        # 从下到上打印一行
        if start < endX and start < endY-1:
            for i in range(endY-1, start, -1):
                number = matrix[i][start]
                print(number, ' ', end='')

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