#include<cstdio> #include<cstring> #include<iostream> #include<algorithm> const int maxn=2000010,maxm=maxn<<1; using namespace std; int n,m,pre[maxm],now[maxn],son[maxm],tot,c[maxn],a[maxn],ans; bool ok;char ch; void read(int &x){ for (ok=0,ch=getchar();!isdigit(ch);ch=getchar()) if (ch==‘-‘) ok=1; for (x=0;isdigit(ch);x=x*10+ch-‘0‘,ch=getchar()); if (ok) x=-x; } void add(int a,int b){pre[++tot]=now[a],now[a]=tot,son[tot]=b;} void dfs(int x){ for (int y=now[x];y;y=pre[y]) dfs(son[y]); int cnt=0; for (int y=now[x];y;y=pre[y]) a[++cnt]=c[son[y]]; sort(a+1,a+1+cnt); for (int i=1;i<=cnt;i++){ if (c[x]+a[i]-1>m) break; c[x]+=(a[i]-1),ans++; } } int main(){ scanf("%d%d",&n,&m); for (int i=1;i<=n;i++) read(c[i]); for (int i=1,x,num;i<=n;i++){ read(num),c[i]+=num; for (int j=1;j<=num;j++) read(x),x++,add(i,x); } dfs(1),printf("%d\n",ans); //for (int i=1;i<=n;i++) printf("%d %d %d\n",i,f[i],g[i]); return 0; } 小结：对于这种贪心的题，我们还是需要证明一下的... ...
原文：https://www.cnblogs.com/ShuraK/p/9277668.html