Pascal's Triangle II in C++

Suppose we have a non-negative index k where k ≤ 33, we have to find the kth index row of Pascal's triangle.

So, if the input is like 3, then the output will be [1,3,3,1]

To solve this, we will follow these steps −

• Define an array pascal of size rowIndex + 1 and fill this with 0

• for initialize r := 0, when r <= rowIndex, update (increase r by 1), do −

  • pascal[r] := 1, prev := 1

  • for initialize i := 1, when i < r, update (increase i by 1), do −

    • cur := pascal[i]

    • pascal[i] := pascal[i] + prev

    • prev := cur

• return pascal

Example 

Let us see the following implementation to get better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
void print_vector(vector<auto> v){
   cout << "[";
   for(int i = 0; i<v.size(); i++){
      cout << v[i] << ", ";
   }
   cout << "]"<<endl;
}
class Solution {
public:
   vector<int> getRow(int rowIndex) {
      vector<int> pascal(rowIndex + 1, 0);
      int prev, cur, r, i;
      for (r = 0; r <= rowIndex; r++) {
         pascal[r] = prev = 1;
         for (i = 1; i < r; i++) {
            cur = pascal[i];
            pascal[i] += prev;
            prev = cur;
         }
      }
      return pascal;
   }
};
main(){
   Solution ob;
   print_vector(ob.getRow(3));
}

Input

3

Output

[1, 3, 3, 1, ]