Code for petrol pump of jump questions

int Solution::jump(vector<int> &a) {
    int jmp = 0;
    int cur = 0;
    int next = 0;
    for(int i = 0; i <= cur; ++ i){
        if(i == a.size()-1)return jmp;
        next = max(next,a[i]+i);
        if(i == cur){
            ++jmp;
            cur = next;
        }
    }
    return -1;
}