59. Spiral Matrix II

Given a positive integer n, generate an n x n matrix filled with elements from 1 to n2 in spiral order.

 

Example 1:

Input: n = 3
Output: [[1,2,3],[8,9,4],[7,6,5]]

Example 2:

Input: n = 1
Output: [[1]]

 

Constraints:

• 1 <= n <= 20

The solution to the above question is

class Solution {

public:

    vector<vector<int>> generateMatrix(int n) {

        vector<vector<int>>v(n,vector<int>(n,-1));

        int SR=0,ER=v.size()-1;

        int SC=0, EC=v[0].size()-1;

        int count=1;

        int a=n*n;

        // cout<<a;

        vector<int>ans;

        while(SR<=ER && SC<=EC){

            for(int i=SC; i<=EC; i++){

                // ans.push_back(v[SR][i]);

                v[SR][i]=(count);

                count++;

                if(count>a){

                return v;

            }

            }

            SR++;

            

            for(int i=SR;i<=ER; i++){

               (v[i][EC]=count);

                count++;

                if(count>a){

                return v;

            }

            }

            EC--;

            

            for(int i=EC; i>=SC; i--){

               (v[ER][i])=count;

                count++;

                if(count>a){

                return v;

            }

            }

            ER--;

            

            for(int i=ER; i>=SR; i--){

                (v[i][SC])=count;

                count++;

                if(count>a){

                return v;

            }

            }

            SC++;

            

        }

        return v;

    }

};