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 ]
]

题解：

class Solution {
public:
  void getSpiralOrder(int n, int k, vector<vector<int>> &res, int l, int r, int u, int d) {
    if (l == r && u == d) {
      res[u][l] = k++;
    }
    else {
      for (int i = l; i < r; i++) {
        res[u][i] = k++;
      }
      for (int i = u; i < d; i++) {
        res[i][r] = k++;
      }
      for (int i = r; i > l; i--) {
        res[d][i] = k++;
      }
      for (int i = d; i > u; i--) {
        res[i][l] = k++;
      }
    }
    if (k > n) {
        return;
    }
    getSpiralOrder(n, k, res, l + 1, r - 1, u + 1, d - 1);
  }

    vector<vector<int>> generateMatrix(int n) {
        if (n == 0) {
            return {};
        }
        if (n == 1) {
            return {{1}};
        }
        vector<vector<int>> res(n, vector<int>(n, 0));
        getSpiralOrder(n * n, 1, res, 0, n - 1, 0, n - 1);
        return res;
    }
};