Staircase

 Staircase

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A child is running up a staircase with N steps, and can hop either 1 step, 2 steps or 3 steps at a time. Implement a method to count how many possible ways the child can run up to the stairs. You need to return number of possible ways W.

Input format :

Integer N

Output Format :

Integer W

Constraints :

1 <= N <= 30

Sample Input 1 :

4

Sample Output 1 :

7

Sample Input 2 :

5

Sample Output 2 :

13

int staircase(int n){
    /* Don't write main().
     *  Don't read input, it is passed as function argument.
     *  Return output and don't print it.
     *  Taking input and printing output is handled automatically.
     */
    if(n<0) return 0;
    if(n==0) return 1;
    return staircase(n-1)+staircase(n-3)+staircase(n-2);
    
    
}

#include <iostream>
using namespace std;

int staircase(int n){
    /* Don't write main().
     *  Don't read input, it is passed as function argument.
     *  Return output and don't print it.
     *  Taking input and printing output is handled automatically.
     */
    if(n<0) return 0;
    if(n==0) return 1;
    return staircase(n-1)+staircase(n-3)+staircase(n-2);
    
    
}
int main() {
    int n, output;
    cin >> n;
    output=staircase(n);
    cout<< output <<endl;
}