run up

/*** 9.1
A child is running up a staircase with n steps, and can hop either 1 step, 2 steps
or 3 steps at atime. Implement a method to count how many possible ways the child can run up the stairs.
IDEA: n steps {1, 2, 3}
***/

#include<iostream>

using namespace std;

int runup(int n) {
       if(n == 0) return 1;
       if(n < 0) return 0;

       return runup(n-1) + runup(n-2) + runup(n-3);

}

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