剑指offer---顺时针打印矩阵

题目：顺时针打印矩阵

要求：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4 X 4矩阵： 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.

class Solution {
public:
    vector<int> printMatrix(vector<vector<int> > matrix) {

    }
};

解题代码：

class Solution {
public:
    vector<int> printMatrix(vector<vector<int> > matrix) {
        int rows = matrix.size();
        int cols = matrix[0].size();
        vector<int> res;

        int start = 0;
        while(cols > start * 2 && rows > start * 2){
            printMatrixInCircle(matrix, rows, cols, start, res);
            start++;
        }
        return res;
    }

private:
    void printMatrixInCircle(vector<vector<int> > matrix, int rows, int cols, int start, vector<int> &res){
        int endX = cols - 1 - start;
        int endY = rows - 1 - start;
        
        // 从左到右
        for(int i = start; i <= endX; i++)
            res.push_back(matrix[start][i]);

        // 从上到下
        if(start < endY){
            for(int i = start + 1; i <= endY; i++)
                res.push_back(matrix[i][endX]);
        }

        // 从右到左
        if(start < endX && start < endY){
            for(int i = endX - 1; i >= start; i--)
                res.push_back(matrix[endY][i]);
        }

        // 从下到上
        if(start < endX && start < endY - 1){
            for(int i = endY - 1; i > start; i--)
                res.push_back(matrix[i][start]);
        }
    }
};