[剑指offer] 29. 顺时针打印矩阵 (for循环条件)

思路：

先定义左上和右下角点坐标，打印可分为从左到右，从上到下，从右到左，从下到上。依次判断最后一圈的四个循环条件。

#include "../stdafx.h"
#include <stdio.h>
#include <stdlib.h>
#include <vector>
#include <iostream>
using namespace std;


vector<int> printMatrix(vector<vector<int> > matrix) {
    vector <int> res;
    int row = matrix.size(); // 行数
    int col = matrix[0].size();  //列数
    if (row == 0 || col == 0)
        return res;
    int left = 0, right = col - 1, top = 0, bottom = row - 1;  
    while (left <= right&&top <= bottom){   //循环大条件
        for (int i = left; i <= right; i++)     
            res.push_back(matrix[top][i]);
        if (bottom-top >= 1){      //从上到下的打印条件
            for (int i = top+1; i <= bottom; i++)
                res.push_back(matrix[i][right]);
        }
        if ((bottom - top >= 1 && (right - left >= 1))){  //右到左条件
            for (int i = right- 1; i >= left; i--)
                res.push_back(matrix[bottom][i]);
        }
        if ((bottom - top >= 2 && (right - left >= 1))){  //下到上条件，注意for循环里i！=top
            for (int i = bottom - 1; i > top; i--)
                res.push_back(matrix[i][left]);
        }
        left++; right--; top++; bottom--;  
    }
    return res;
}

int main(void){
    vector<vector<int>> array = { { 1, 2, 3, 4 }, { 5, 6, 7, 8 }, { 9, 10, 11, 12 }, {13,14,15,16} };
    vector<int>vec = printMatrix(array);

    vector <int>:: iterator it;
    for (it = vec.begin(); it != vec.end();it++)
        cout << *it << endl;


    getchar();
    return 0;
}