Key cutting

#include<iostream>
#include<vector>
typedef long long ll;
using namespace std;

void decrease(vector<ll>& key, ll a, ll b, ll minim){
    for(ll i=a; i<=b; i++){
        key[i] -= minim;
    }
    
}

int main(){
    ll n;
    cin >> n;
    vector<ll> key(n);

    for(ll i = 0; i < n; ++i) cin >> key[i];

    ll start = -1;
    ll minim;

    ll op = 0;
    for(ll i = 0; i < n; i++){
        if(start == -1 and key[i]!=0){
            start = i;
            minim = key[i];
        }

        if(start!=-1 and (key[i]==0 or i==n-1)){
            //cout << "jansdjkak" << endl;
            // cout << minim << "aksdjla" << endl;
            if(key[i]==0) decrease(key,start,i-1,minim);
            else decrease(key,start,i,minim);
            start = -1;
            op +=1;
            i=0;

        }
        if(start!=-1 and key[i]<minim) minim = key[i];

    }
    cout << op << endl;
    

}

/*1 3 2 4 1
0 2 1 3 0
0 1 0 2 0
0 0 0 2 0
0 0 0 0 0
*/

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: ACCEPTED

Test 10

Verdict: TIME LIMIT EXCEEDED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: TIME LIMIT EXCEEDED

Test 13

Verdict: TIME LIMIT EXCEEDED

Test 14

Verdict: TIME LIMIT EXCEEDED