19.2.9 [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 ]
]

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        int dir[4][2] = { 0,1,1,0,0,-1,-1,0 }, dire = 0, x = 0, y = 0;
        vector<vector<int>>ans(n, vector<int>(n, -1));
        for (int i = 1; i <= (n * n); i++) {
            ans[x][y] = i;
            int nextx = x + dir[dire][0], nexty = y + dir[dire][1];
            if (nextx >= n || nextx < 0 || nexty >= n || nexty < 0 || ans[nextx][nexty] != -1) {
                dire = (dire + 1) % 4;
                nextx=x+dir[dire][0], nexty = y + dir[dire][1];
            }
            x = nextx, y = nexty;
        }
        return ans;
    }
};