题目链接：http://codeforces.com/contest/283/problem/B

思路： dp[now][flag]表示现在在位置now，flag表示是接下来要做的步骤，然后根据题意记忆化搜索记忆，vis数组标记那些已经访问过的状态。

#include <iostream>

#include <cstdio>

#include <cstring>

#include <algorithm>

#define REP(i, a, b) for (int i = (a); i < (b); ++i)

#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)

using namespace std;

const int MAX_N = (200000 + 100);

long long dp[MAX_N][2];

int vis[MAX_N][2];

int N, a[MAX_N];

long long dfs(int now, int dir)

{

    if (now <= 0 || now > N) return 0;

    if (~dp[now][dir]) return dp[now][dir];

    if (vis[now][dir]) return -1;

    vis[now][dir] = 1;

    long long res = dfs(dir ? now + a[now] : now - a[now], dir ^ 1);

    return dp[now][dir] = (res < 0 ? -1 : res + a[now]);

}

int main()

{

    while (cin >> N) {

        FOR(i, 2, N) cin >> a[i];

        memset(dp, -1, sizeof(dp));

        memset(vis, 0, sizeof(vis));

        FOR(i, 1, N - 1) {

            long long ans = dfs(i + 1, 0);

            cout << (ans < 0 ? -1 : ans + i) << endl;

        }

    }

    return 0;

}