pascals-triangle-ii.cpp

/*APPROACH
for e.g for 4th row 4Co=1 4C1=4 4C2=6 4C3=4 4C4=1  {short tips & formulae: remember nC0=1 nCn=1 nC1=n always}
        
                   0  1  2  3  4        j columns
i rows
i=0                       1
i=1                     1   1
i=2                   1   2   1
i=3                 1   3   3   1
i=4               1   4   6   4   1

nC(r+1)-> nCr*Factor

4Co=1 4C1=4 4C2=6 4C3=4 4C4=1
Factor= nC(r+1)/nCr  ----> (n-r)/(r+1)  replace n with i & r with j


*/

class Solution {
public:
    vector<int> getRow(int i) {
        vector<int> ans;
        long val = 1;

        for ( int j = 0; j <= i; j++ ) {
            ans.push_back(val);
            val = val * (i-j) / (j+1); // (i-j)/(j+1) is a factor
        }
        return ans; 
    }
};