59. Spiral Matrix II

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 ]
]

题意：给一个数n，按螺旋方式把 值1--n^2之间的数填入矩阵。
思路：跟spiral matrix题目一样，重点是对matrix的螺旋式遍历方法。

class Solution {
public:
vector<vector<int>> generateMatrix(int n) {
vector<vector<int>> matrix(n, vector<int>(n));
if (n < 1)
return matrix;
int i = 0;
int j = 0;
int count = 1;
matrix[i][j] = count++;
const int nn = n*n;
while (count <= nn){
//turn right
while (j + 1 < n - i && count <= nn){
matrix[i][++j] = count++;
}
//turn down
while (i + 1 < n - (n - j - 1) && count <= nn){
matrix[++i][j] = count++;
}
//turn left
while (j - 1 >= n - i - 1 && count <= nn){
matrix[i][--j] = count++;
}
//turn up
while (i - 1 >= j + 1 && count <= nn){
matrix[--i][j] = count++;
}
}
return matrix;
}
};