Spiral Matrix II.cpp

/* 

    Solution by Rahul Surana
    
    ***********************************************************


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



    ***********************************************************
*/


#include <bits/stdc++.h>

class Solution {
public:
   vector<vector<int>> generateMatrix(int n) {
        int r1 = 0, r2 = n-1;
        int c1 = 0, c2 = n-1;
        int val = 0;
        
        vector<vector<int>> v(n, vector<int> (n));
        while(r1 <= r2 && c1 <= c2)
        {
            for(int i = c1; i <= c2; ++i) v[r1][i] = ++val;
                
            for(int i = r1+1; i <= r2; ++i) v[i][c2] = ++val;
            if(r1 < r2 && c1 < c2)
            {
                for(int i = c2-1; i>c1; --i)
                    v[r2][i] = ++val;
                for(int i = r2; i > r1; --i) 
                    v[i][c1] = ++val;
            }
            ++r1;
            --r2;
            ++c1;
            --c2;
        }
        return v;
    }
};