#3052. 「十二省联考 2019」春节十二响 [启发式合并]

考虑是左边有链右边有链的情况，肯定是取max，次max，次次max（雾
然后你可以把一棵树当做是若干条链，启发式合并，这题就做完了

// powered by c++11
// by Isaunoya
#include <bits/stdc++.h>
#define rep(i, x, y) for (register int i = (x); i <= (y); ++i)
#define Rep(i, x, y) for (register int i = (x); i >= (y); --i)
using namespace std;
using db = double;
using ll = long long;
using uint = unsigned int;
#define Tp template
using pii = pair<int, int>;
#define fir first
#define sec second
Tp<class T> void cmax(T& x, const T& y) {if (x < y) x = y;} Tp<class T> void cmin(T& x, const T& y) {if (x > y) x = y;}
#define all(v) v.begin(), v.end()
#define sz(v) ((int)v.size())
#define pb emplace_back
Tp<class T> void sort(vector<T>& v) { sort(all(v)); } Tp<class T> void reverse(vector<T>& v) { reverse(all(v)); }
Tp<class T> void unique(vector<T>& v) { sort(all(v)), v.erase(unique(all(v)), v.end()); }
const int SZ = 1 << 23 | 233;
struct FILEIN { char qwq[SZ], *S = qwq, *T = qwq, ch;
#ifdef __WIN64
#define GETC getchar
#else
  char GETC() { return (S == T) && (T = (S = qwq) + fread(qwq, 1, SZ, stdin), S == T) ? EOF : *S++; }
#endif
  FILEIN& operator>>(char& c) {while (isspace(c = GETC()));return *this;}
  FILEIN& operator>>(string& s) {while (isspace(ch = GETC())); s = ch;while (!isspace(ch = GETC())) s += ch;return *this;}
  Tp<class T> void read(T& x) { bool sign = 0;while ((ch = GETC()) < 48) sign ^= (ch == 45); x = (ch ^ 48);
    while ((ch = GETC()) > 47) x = (x << 1) + (x << 3) + (ch ^ 48); x = sign ? -x : x;
  }FILEIN& operator>>(int& x) { return read(x), *this; } FILEIN& operator>>(ll& x) { return read(x), *this; }
} in;
struct FILEOUT {const static int LIMIT = 1 << 22 ;char quq[SZ], ST[233];int sz, O;
  ~FILEOUT() { flush() ; }void flush() {fwrite(quq, 1, O, stdout); fflush(stdout);O = 0;}
  FILEOUT& operator<<(char c) {return quq[O++] = c, *this;}
  FILEOUT& operator<<(string str) {if (O > LIMIT) flush();for (char c : str) quq[O++] = c;return *this;}
  Tp<class T> void write(T x) {if (O > LIMIT) flush();if (x < 0) {quq[O++] = 45;x = -x;}
        do {ST[++sz] = x % 10 ^ 48;x /= 10;} while (x);while (sz) quq[O++] = ST[sz--];
  }FILEOUT& operator<<(int x) { return write(x), *this; } FILEOUT& operator<<(ll x) { return write(x), *this; }
} out;
#define int long long
int n ;
const int maxn = 2e5 + 52 ;
int a[maxn] , fa[maxn] ;
priority_queue < int > q[maxn] ;
int top = 0 , st[maxn] ;
void merge(int x , int y) {
    while(q[x].size() && q[y].size()) {
        st[++ top] = max(q[x].top() , q[y].top()) ;
        q[x].pop() , q[y].pop() ;
    }
    if(q[y].size())
        swap(q[x] , q[y]) ;
    while(top) q[x].push(st[top --]) ;
}
signed main() {
  // code begin.
    in >> n ;
    rep(i , 1 , n) 
        in >> a[i] ;
    rep(i , 2 , n)
        in >> fa[i] ;
    Rep(i , n , 2) {
        q[i].push(a[i]) ;
        merge(fa[i] , i) ;
    }
    int ans = a[1] ;
    while(! q[1].empty()) ans += q[1].top() , q[1].pop() ;
    out << ans << '\n' ;
    return 0;
  // code end.
}

#3052. 「十二省联考 2019」春节十二响 [启发式合并]

原文：https://www.cnblogs.com/Isaunoya/p/12382017.html