Leetcode 细节实现题 Spiral Matrix II

Spiral Matrix II

 Total Accepted: 12773 Total
Submissions: 41526My Submissions

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：将数值 1 到n^2以螺旋顺序放到到一个方阵中

思路：

从左到右，从上到下，从右到左，从下到上按顺序遍历放数值

将矩阵的(0,0)元素看成坐标原点，向右为x轴正方向，向下为y轴正方向

用四个变量，即两个坐标(startx, starty), (endx, endy) 表示每轮遍历的矩阵的左上角和右下角的坐标

复杂度：O(n^2)

vector<vector<int> > generateMatrix(int n){
vector<vector<int> > matrix(n, vector<int>(n));
int startx = 0, starty = 0;
int endx = n - 1, endy = n - 1;
for(int k = 1; k <= n * n; ){
for(int j = startx; j <= endx; ++j) matrix[starty][j] = k++;
starty++;
for(int i = starty; i <= endy; ++i) matrix[i][endy] = k++;
endx--;
for(int j = endx; j >= startx; --j) matrix[endy][j] = k++;
endy--;
for(int i = endy; i >= starty; --i) matrix[i][startx] = k++;
startx++;
}
return matrix;
}