54. Spiral Matrix

题目

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

[
[ 1, 2, 3 ],
[ 4, 5, 6 ],
[ 7, 8, 9 ]
]
You should return [1,2,3,6,9,8,7,4,5].

思路

本题思路很简单,但是就是写起来复杂，是真的复杂，很容易写错，主要思路如下:

建立四个变量分别为int rowbegin = 0,rowend=matrix.size()-1,colbegin=0,colend = matrix[0].size()-1;
然后按照从左往右，从上至下，从右往左，从下至上的顺序，不断循环；
满足条件，跳出循环，并返回

代码

class Solution {public:    vector<int> spiralOrder(vector<vector<int>>& matrix) {        vector<int> res;        if (matrix.empty())            return res;         int rowbegin = 0,rowend=matrix.size()-1,colbegin=0,colend = matrix[0].size()-1;                while(rowbegin<=rowend&&colbegin<=colend)//大循环        {            for(int i=colbegin;i<=colend;i++)//从左往右            {                res.push_back(matrix[rowbegin][i]);            }            rowbegin++;            for(int i=rowbegin;i<=rowend;i++)//从上至下            {                res.push_back(matrix[i][colend]);            }            colend--;            if(rowbegin<=rowend)            {                for(int i=colend;i>=colbegin;i--)//从右往左                {                    res.push_back(matrix[rowend][i]);                }            }            rowend--;            if(colbegin<=colend)            {                for(int i=rowend;i>=rowbegin;i--)//从下往上                {                    res.push_back(matrix[i][colbegin]);                }            }            colbegin++;        }        return res;    }};