leetcode 59. Spiral Matrix II

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

Example:

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

思路：一次填充矩阵外围一轮数。

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int> > res(n, vector<int>(n, 0));
        int res[n][n];
        int **res = new int* [n];
        for (int i = 0; i < n; i++)
            
        int num = n * n;
        int cnt = 1;
        int start_row = 0, start_col = 0, end_row = n - 1, end_col = n - 1; 
        while (cnt <= num) {
            for (int j = start_col; j <= end_col; j++) {
                res[start_row][j] = cnt++;
            }
            for (int i = start_row + 1; i <= end_row; i++) {
                res[i][end_col] = cnt++;
            }
            for (int j = end_col - 1; j >= start_col; j--) {
                res[end_row][j] = cnt++;
            }
            for (int i = end_row - 1; i > start_row; i--) {
                res[i][start_col] = cnt++;
            }
            start_row++;
            start_col++;
            end_row--;
            end_col--;
        }
        return res;
    }
};