generateMatrix.cpp

#include <vector>
using namespace std;

class Solution
{
public:
    vector<vector<int>> generateMatrix(int n)
    {
        if (n <= 0) return vector<vector<int>>();
        // 这是一个拥有n²个元素，n行n列的矩阵

        int left = 0;
        int right = n - 1;
        int up = 0;
        int down = n - 1;
        // 扩容！
        vector<vector<int>> res(n,vector<int>(n));
        int currentValue = 1;

        while (currentValue <= n*n)
        {
            for (int i = left;i <= right;i++)
            {
                res[up][i] = currentValue;
                currentValue++;
            }
            up++;
            for (int i = up;i <= down;i++)
            {
                res[i][right] = currentValue;
                currentValue++;
            }
            right--;

            for (int i = right;i >= left;i--)
            {
                res[down][i] = currentValue;
                currentValue++;
            }
            down--;
            for (int i = down;i >= up;i--)
            {
                res[i][left] = currentValue;
                currentValue++;
            }
            left++;
        }

        return res;
    }
};