LeetCode 59. Spiral Matrix II

n, generate a square matrix filled with elements from 1 to n2

For example,

Given n = 3,

You should return the following matrix:

[ [ 1, 2, 3 ], [ 8, 9, 4 ], [ 7, 6, 5 ] ]

answer:

class Solution {
public:
    vector<vector<int>> generateMatrix(int n) {
        
        vector<vector<int>> result;
        if(n == 0) return result;
        else if( n < 0) n = -n;
        //result.reserve(n);
        vector<int> temp;
        for(int i = 0; i < n; i ++)
            temp.push_back(0);
        for(int i = 0; i < n; i ++)
            //result[i].reserve(n);
            result.push_back(temp);
        int left = 0, right = n - 1, length = n;
        int index = 0;
        while(length > 0){
            for(int i = 0; i < length; i ++){
                result[left][left + i] = ++ index;
            }
            cout << index << endl;
            for(int i = 1; i < length; i ++){
                result[left + i][right] = ++ index;
            }
            cout << index << endl;
            for(int i = 1; i < length; i ++){
                result[right][right - i] = ++ index;
            }
            cout << index << endl;
            for(int i = 1; i < length - 1; i ++){
                result[right - i][left] = ++ index;
            }
            cout << index << endl;
            length -= 2;
            left ++;
            right --;
        }
        return result;
    }
};