very simple and uderstable solution with cpp

string fairRations(vector B) {

int key=0;

for(int i = 0;i < B.size()-1;i++){ // because lin last element we have to do other operation
    if(i == B.size()-1){  //this is for last element only
        if(B[i] % 2!=0){
             B[i]++;
             B[i-1]++;
        }

    }
    if( B[i] % 2 !=0){
        B[i]++;
        B[i+1]++;
        key+=2;

    }
}
bool flag = 1;

for(int i = 0;i < B.size() ; i++){
    if(B[i] % 2!=0){
        flag=0;
        break;
    }
}


if( flag ==0){
    return "NO";
}
else{
    return to_string(key);
}

}