codeforces B. Cow Program (记忆化搜索)

题目链接：

题目大意：

题目分析：

AC代码：

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#define MAX 200007

using namespace std;

typedef long long LL;

LL dp[MAX][2];
int vis[MAX][2];
int a[MAX],n;

void dfs ( int x , int d )
{
if ( vis[x][d%2] ) return;
vis[x][d%2] = 1;
if ( d&1 )
{
int y = x-a[x];
if ( y <= 0 )
{
dp[x][d%2] = a[x];
return;
}
dfs ( y , d+1 );
if ( dp[y][(d+1)%2] != -1 )
dp[x][d%2] = dp[y][(d+1)%2] + a[x];
}
else
{
int y = x+a[x];
if ( y > n )
{
dp[x][d%2] = a[x];
return;
}
dfs ( y , d+1 );
if ( dp[y][(d+1)%2] != -1 )
dp[x][d%2] = dp[y][(d+1)%2] + a[x];
}
}

int main ( )
{
while ( ~scanf ( "%d" , &n ) )
{
for ( int i = 2 ; i <= n ; i++ )
scanf ( "%d" , &a[i] );
memset ( vis , 0 , sizeof ( vis ) );
memset ( dp , -1, sizeof ( dp ) );
dp[1][0] = -1;
vis[1][0] = 1;
dp[1][1] = 0;
vis[1][1] = 1;
for ( int i = 2 ; i <= n ; i++ )
dfs ( i , 1 );
for ( int i = 2 ; i <= n ; i++ )
if ( dp[i][1] != -1 )
dp[i][1] += i-1;
for ( int i = 2 ; i <= n ; i++ )
printf ( "%lld\n" , dp[i][1] );
}
}