《剑指offer》第二十九题：顺时针打印矩阵

// 面试题29：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。

#include <cstdio>

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

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

    int start = 0; //每圈的开始起点
    while (columns > start * 2 && rows > start * 2) //当前圈存在
    {
        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;

    //从左到右打印圈第一行
    for (int i = start; i <= endX; ++i)
    {
        int number = numbers[start][i];
        printNumber(number);
    }

    //从上到下打印圈右列
    if (start < endY) //右列存在条件, 两列
    {
        for (int i = start + 1; i <= endY; ++i)
        {
            int number = numbers[i][endX];
            printNumber(number);
        }
    }

    //从右到左打印圈第二行
    if (start < endX && start < endY) //两行两列
    {
        for (int i = endX - 1; i >= start; --i)
        {
            int number = numbers[endY][i];
            printNumber(number);
        }
    }


    //从下到上打印圈左列
    if (start < endY - 1 && start < endX) //三行两列
    {
        for (int i = endY - 1; i > start; --i)
        {
            int number = numbers[i][start];
            printNumber(number);
        }
    }
}

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

}

// ====================测试代码====================
void Test(int columns, int rows)
{
    printf("Test Begin: %d columns, %d rows.
", columns, rows);

    if (columns < 1 || rows < 1)
        return;

    int** numbers = new int* [rows];
    for (int i = 0; i < rows; ++i)
    {
        numbers[i] = new int[columns];
        for (int j = 0; j < columns; ++j)
        {
            numbers[i][j] = i * columns + j + 1;
        }
    }

    PrintMatrixClockwisely(numbers, columns, rows);
    printf("
");

    for (int i = 0; i < rows; ++i)
        delete[](int*)numbers[i];

    delete[] numbers;
}

int main(int argc, char* argv[])
{
    /*
    1
    */
    Test(1, 1);

    /*
    1    2
    3    4
    */
    Test(2, 2);

    /*
    1    2    3    4
    5    6    7    8
    9    10   11   12
    13   14   15   16
    */
    Test(4, 4);

    /*
    1    2    3    4    5
    6    7    8    9    10
    11   12   13   14   15
    16   17   18   19   20
    21   22   23   24   25
    */
    Test(5, 5);

    /*
    1
    2
    3
    4
    5
    */
    Test(1, 5);

    /*
    1    2
    3    4
    5    6
    7    8
    9    10
    */
    Test(2, 5);

    /*
    1    2    3
    4    5    6
    7    8    9
    10   11   12
    13   14   15
    */
    Test(3, 5);

    /*
    1    2    3    4
    5    6    7    8
    9    10   11   12
    13   14   15   16
    17   18   19   20
    */
    Test(4, 5);

    /*
    1    2    3    4    5
    */
    Test(5, 1);

    /*
    1    2    3    4    5
    6    7    8    9    10
    */
    Test(5, 2);

    /*
    1    2    3    4    5
    6    7    8    9    10
    11   12   13   14    15
    */
    Test(5, 3);

    /*
    1    2    3    4    5
    6    7    8    9    10
    11   12   13   14   15
    16   17   18   19   20
    */
    Test(5, 4);

    return 0;
}

分析：画图举例很方便，可以直观的算出各种条件。注意条件不要写错了。

---

牛客网给出了容器vector，注意：

int rows = (int)matrix.size();
int columns = (int)matrix[0].size();

class Solution {
public:
    vector<int> printMatrix(vector<vector<int>> matrix) {
        
        int start = 0;
        int rows = (int)matrix.size();
        int columns = (int)matrix[0].size();
        vector<int> printNumber;
        
        if (rows == 0 || columns == 0)
            return printNumber;
        
        while (columns > start * 2 && rows > start * 2)
        {
            int endX = columns - 1 - start;
            int endY = rows - 1 - start;

            for (int i = start; i <= endX; ++i)
            {
                int number = matrix[start][i];
                printNumber.push_back(number);
            }
            if (start < endY)
            {
                for (int i = start + 1; i <= endY; ++i)
                {
                    int number = matrix[i][endX];
                    printNumber.push_back(number);
                }
            }
            if (start < endX && start < endY)
            {
                for (int i = endX - 1; i >= start; --i)
                {
                    int number = matrix[endY][i];
                    printNumber.push_back(number);
                }
            }
            if (start < endX && start < endY - 1)
            {
                for (int i = endY - 1; i > start; --i)
                {
                    int number = matrix[i][start];
                    printNumber.push_back(number);
                }
            }
            ++start;
        }
        return printNumber;
    }
};