Solution to the problem 'Counting Valleys' from HackerRank

 question link: https://www.hackerrank.com/challenges/counting-valleys/problem

#include <bits/stdc++.h>

#define int long long

#define pb push_back

#define fi first

#define se second

#define pii pair<int,int>

using namespace std;

int32_t main()

{

    ios_base::sync_with_stdio(false);

    cin.tie(NULL);

    cout.tie(NULL);

    int n,ans=0;

    cin>>n;

    vector<int> hike;

    int prefix[n];

    for(int i=0;i<n;i++){

        char a;

        cin>>a;

        if(a=='U') hike.pb(1);

        else hike.pb(-1);

    }

    prefix[0]=hike[0];

    for(int i=1;i<n;i++) prefix[i]=prefix[i-1]+hike[i];

    for(int i=1;i<n;i++){

        if(prefix[i]==0&&prefix[i-1]==-1) ans++;

    }

    cout<<ans;

    return 0;

}