剑指offer - 顺时针打印矩阵

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。例如，如果输入如下矩阵

2019-05-17-162435.jpg

算法实现

#include <iostream>
using namespace std;

void PrintMatrixInCircle(int **numbers, int columns, int rows, int start);
void printNumber(int number);

// numbers 矩阵 columns列 rows行
void PrintMatrixClockwisely(int **numbers, int columns, int rows) {
    if (numbers == nullptr || columns <= 0 || rows <= 0)
        return;

    int start = 0; // 开始位置

    while (columns > start*2 && rows > start*2) {
        PrintMatrixInCircle(numbers, columns, rows, start);
        ++start;
    }
}

void PrintMatrixInCircle(int **numbers, int columns, int rows, int start) {
    int endX = columns - 1 - start;
    int endY = rows - 1 - start;

    // 从左到右打印一行
    for (int i=start; i <= endX; ++i) {
        int number = numbers[start][i];
        printNumber(number);
    }

    // 从上到下打印一列
    if (start < endY) {
        for (int i = start + 1; i <= endY; ++i) {
            int number = numbers[i][endX];
           printNumber(number);
        }
    }

    // 从右到左打印一行
    if (start < endX && start < endY) {
        for (int i=endX - 1; i>=start; --i) {
            int number = numbers[endY][i];
            printNumber(number);
        }
    }

    // 从上到下打印一列
    if (start<endX && start < endY - 1) {
        for (int i = endY - 1; i >= start + 1; --i) {
            int number = numbers[i][start];
            printNumber(number);
        }
    }
}

void printNumber(int number)
{
    printf("%d\t", number);
}

使用vector实现

vector<int> printMatrix(vector<vector<int> > matrix) {
   unsigned long row = matrix.size();
   unsigned long col = matrix[0].size();
   vector<int> res;

    // 输入的二维数组非法，返回空的数组
    if (row == 0 || col == 0)  return res;

    // 定义四个关键变量，表示左上和右下的打印范围
    int left = 0, top = 0, right = col - 1, bottom = row - 1;
    while (left <= right && top <= bottom)
    {
        // left to right
        for (int i = left; i <= right; ++i)  res.push_back(matrix[top][i]);
        // top to bottom
        for (int i = top + 1; i <= bottom; ++i)  res.push_back(matrix[i][right]);
        // right to left
        if (top != bottom)
            for (int i = right - 1; i >= left; --i)  res.push_back(matrix[bottom][i]);
        // bottom to top
        if (left != right)
            for (int i = bottom - 1; i > top; --i)  res.push_back(matrix[i][left]);

        left++;
        top++;
        right--;
        bottom--;
    }
    return res;
}

参考

《剑指offer》
顺时针打印矩阵