#数组 #螺旋矩阵 #leetcode

spiral-matrix-ii-59.cpp

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        // 行 列
        vector<vector<int>> mat;
        for (int i = 0; i < n; ++i) {
            vector<int> tmp;
            for (int j = 0; j < n; ++j)
                tmp.push_back(0);
            mat.push_back(tmp);
        }
        assert(mat.size() == n && "mat size not equal to n");
        
        // right down left up
        int step[4][2] = {{0,1}, {1,0}, {0, -1}, {-1,0}};

        int size = n * n;
        int num = 1;

        int row = 0, col = 0;
        int k_step = 0;
        while (num <= size) {
            mat.at(row).at(col) = num++;
            int next_row = row + step[k_step][0];
            int next_col = col + step[k_step][1];

            if (next_row < 0 || next_row >= n || next_col < 0 || next_col >= n)
                k_step = (k_step + 1) % 4;
            else if (mat.at(next_row).at(next_col) != 0)
                k_step = (k_step + 1) % 4;
            // update
            row = row + step[k_step][0];
            col = col + step[k_step][1];
        }
        return mat;
    }
};