HackerRank 'Connecting Towns' Solution

Martin Kysel · August 4, 2020

Short Problem Definition:

Gandalf is travelling from Rohan to Rivendell to meet Frodo but there is no direct route from Rohan (T1) to Rivendell (Tn).

But there are towns T2,T3,T4…Tn-1 such that there are Ni routes from Town T1 to T2, and in general, Ni routes from Ti to Ti+1 for i=1 to n-1 and 0 routes for any other Ti to Tj for j ≠ i+1

Find the total number of routes Gandalf can take to reach Rivendell from Rohan.

Connecting Towns


time complexity is O(N)

space complexity is O(1)


This is a simple combinatorics problem. Even though python ints don’t overflow easily, I added the MOD anyways. The code in GoLang is also available.

MOD = 1234567

def main():
    t = input()
    for _ in xrange(t):
        n = input()
        arr = map(int, raw_input().split())
        routes = 1
        for value in arr:
            routes = ( routes * value ) % MOD
        print routes
if __name__ == '__main__':

func connectingTowns(n int32, routes []int32) int32 {
    result := int32(1)
    for _, value := range routes {
        result = (result*value) % 1234567
    return result

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