LeetCode:Spiral Matrix II

题目描述：

Given an integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ]]

思路分析：四个for循环分别控制四个方向上数字的填入。

代码：

vector<vector<int> > Solution::generateMatrix(int n){    vector<vector<int> > matrix;    vector<int> line;    int i,j,k;    int count = 1;    for(i = 0;i < n;i++)    {        for(j = 0;j < n;j++)            line.push_back(0);        matrix.push_back(line);        line.clear();    }    for(i = 0;i*2 < n;i++)    {        for(j = i,k = i;k < n - i - 1;k++)            matrix[j][k] = count++;        for(j = i,k = n - 1 - i;j < n - i - 1;j++)            matrix[j][k] = count++;        for(j = n - i - 1,k = n - i - 1;k > i;k--)            matrix[j][k] = count++;        for(j = n - 1 - i,k = i;j > i;j--)            matrix[j][k] = count++;    }    if(n % 2 == 1)        matrix[n/2][n/2] = count++;    return matrix;}