A：显然应该让未确定的大小尽量大。不知道写了啥就wa了一发。
#include<iostream> #include<cstdio> #include<cmath> #include<cstdlib> #include<cstring> #include<algorithm> using namespace std; #define ll long long #define N 200010 #define inf 1000000010 char getc(){char c=getchar();while ((c<'A'||c>'Z')&&(c<'a'||c>'z')&&(c<'0'||c>'9')) c=getchar();return c;} int gcd(int n,int m){return m==0?n:gcd(m,n%m);} int read() { int x=0,f=1;char c=getchar(); while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();} while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar(); return x*f; } int n,p[N],fa[N],a[N],s[N],t,ans; bool flag=1; struct data{int to,nxt; }edge[N]; void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;} void dfs(int k) { if (!flag) return; for (int i=p[k];i;i=edge[i].nxt) { int x=edge[i].to,son=0; for (int j=p[x];j;j=edge[j].nxt) son++; if (son==0) a[x]=0; else { int y=inf; for (int j=p[x];j;j=edge[j].nxt) y=min(y,s[edge[j].to]); if (y<s[k]) {flag=0;break;} a[x]=y-s[k];s[x]=s[k]+a[x]; for (int j=p[x];j;j=edge[j].nxt) a[edge[j].to]=s[edge[j].to]-s[x],dfs(edge[j].to); } } } signed main() { #ifndef ONLINE_JUDGE freopen("a.in","r",stdin); freopen("a.out","w",stdout); const char LL[]="%I64d\n"; #endif n=read(); for (int i=2;i<=n;i++) { int x=read();fa[i]=x;addedge(x,i); } for (int i=1;i<=n;i++) s[i]=read(); a[1]=s[1];dfs(1); if (flag) { ll ans=0; for (int i=1;i<=n;i++) ans+=a[i]; cout<<ans; } else cout<<-1; return 0; //NOTICE LONG LONG!!!!! }