Min Jumps Array

• Time : $O(n)$
• Space : $O(1)$

int Solution::jump(vector<int> &A) {
    if(A.size() == 1) return 0;
    int ma = A[0], now = 0, res = 0;
    while(now < A.size() - 1 and now <= ma) {
        if(ma >= A.size() - 1) return res + 1;
        int jump = -1;
        for(int i = now; i <= ma and i < A.size(); i++) jump = max(jump, i + A[i]);
        if(ma >= jump and ma != A.size() - 1) return -1;
        now = ma;
        ma = jump;
        res++;
    }
    return -1;
}