LeetCode 59. 螺旋矩阵 II

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        vector<vector<int>> res = vector<vector<int>>(n, vector<int>(n));
        int m = 1;
        int i = 0, j = 0;
        int left = 0, right = n, up = 1, down = n;
        int num = n * n;
        while (m <= num) {
            while (j < right) {
                res[i][j] = m;
                j++;
                m++;
            }
            if (m > num) return res;
            right--;
            j--;
            i++;
            while (i < down) {
                res[i][j] = m;
                i++;
                m++;
            }
            if (m > num) return res;
            down--;
            i--;
            j--;
            while (j >= left) {
                res[i][j] = m;
                j--;
                m++;
            }
            if (m > num) return res;
            left++;
            j++;
            i--;
            while (i >= up) {
                res[i][j] = m;
                i--;
                m++;
            }
            if (m > num) return res;
            up++;
            i++;
            j++;
        }
        return res;
    }
};