Codeforces Round #174 (Div. 1) B. Cow Program(dp + 记忆化)

来源：互联网发布：linux查看当前php版本编辑：程序博客网时间：2024/06/05 03:31

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;}

0 0