【D - How Many Answers Are Wrong】

Ideas:

• Weighted disjoint-set, interval statistics .

• Weighted disjoint-set and common disjoint-set difference:

  1. Find function can not be written recursively, and to be able to dynamically update all points on the path to Val .
  2. UNION function to change Val [Parr] , you need not change their Val [R & lt] .

• This 题 Note:

  1. Title did not say a multi-set of use cases, you also have to read the end of the file, otherwise it will WA .
  2. Interval statistics need to become left and right to open and close (so for: 6,6,1 class restriction will not wrong).

Code:

• 46ms 2972kB

​//46ms		2972kB


#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int maxn = 200005;

int N,M;
int ans;
int par[maxn];
int val[maxn];//value后缀和

void INIT(){
	memset(par , -1 , sizeof(par));
	memset(val , 0  , sizeof(val));
	ans = 0;
	return ;
}

int FIND(int i){
	if(par[i] == -1)
		return i;
	int temp = par[i];
	par[i] = FIND(par[i]);
	val[i] += val[temp];
	return par[i];
}

int main(){
	while(cin>>N>>M){
		INIT();
		while(M--){
			int l , r , w;
			scanf("%d%d%d" , &l , &r , &w);
			int parl = FIND(l-1) ;
			int parr = FIND(r) ;
			if(parr == parl)
				if(val[l-1] + w != val[r])
					ans++;
				else	;
			else{
				par[parr] = parl;
				val[parr] = val[l-1] + w - val[r] ;
				//为什么不需要改 val[r] : par[r]依然是parr , 且parr和 r之间的势差仍为val[r] 
			}
		}
		printf("%d\n" , ans);
	}
	return 0;
} ​