[HNOI/AHOI2018]道路
那个式子是唬你的
直接考虑倒推
#include<bits/stdc++.h> #define fp(i,a,b) for(register int i=a,I=b+1;i<I;++i) #define fd(i,a,b) for(register int i=a,I=b-1;i>I;--i) #define go(u) for(register int i=fi[u],v=e[i].to;i;v=e[i=e[i].nx].to) #define file(s) freopen(s".in","r",stdin),freopen(s".out","w",stdout) template<class T>inline bool cmax(T&a,const T&b){return a<b?a=b,1:0;} template<class T>inline bool cmin(T&a,const T&b){return a>b?a=b,1:0;} using namespace std; char ss[1<<17],*A=ss,*B=ss; inline char gc(){return A==B&&(B=(A=ss)+fread(ss,1,1<<17,stdin),A==B)?-1:*A++;} template<class T>inline void sd(T&x){ char c;T y=1;while(c=gc(),(c<48||57<c)&&c!=-1)if(c==45)y=-1;x=c-48; while(c=gc(),47<c&&c<58)x=x*10+c-48;x*=y; } const int N=4e4+1; typedef int arr[N]; typedef long long ll; int n,m,Top,Tot;arr a,b,c,s,t,Num,S;ll f[82][41][41]; void dfs(int u,int x,int y){ int p=Num[u]=Top?S[Top--]:++Tot; if(!s[u]){ fp(i,0,x)fp(j,0,y)f[p][i][j]=(ll)c[u]*(a[u]+i)*(b[u]+j); return; } dfs(s[u],x+1,y),dfs(t[u],x,y+1); int ls=Num[s[u]],rs=Num[t[u]]; fp(i,0,x)fp(j,0,y) f[p][i][j]=min(f[ls][i+1][j]+f[rs][i][j],f[ls][i][j]+f[rs][i][j+1]); S[++Top]=ls,S[++Top]=rs; } int main(){ #ifndef ONLINE_JUDGE file("s"); #endif sd(n);m=2*n-1;int u,v; fp(i,1,n-1)sd(u),sd(v),s[i]=u<0?n-1-u:u,t[i]=v<0?n-1-v:v; fp(i,n,m)sd(a[i]),sd(b[i]),sd(c[i]); dfs(1,0,0); printf("%lld\n",f[Num[1]][0][0]); return 0; }