【bzoj1202】 HNOI2005—狡猾的商人

// bzoj1202
#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<cmath>
#define LL long long
#define inf 2147483640
#define Pi 3.1415926535898
#define free(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout);
using namespace std;

int fa[10010],m,n,T,r[10010];

int find(int x) {
    if (x==fa[x]) return x;
    int f=find(fa[x]);
    r[x]=r[x]+r[fa[x]];
    fa[x]=f;
    return f;
}
bool Union(int x,int y,int w) {
    int r1=find(x),r2=find(y);
    if (r1==r2) {
        if (w!=r[y]-r[x]) return 1;}
    else {
        fa[r2]=r1;
        r[r2]=w+r[x]-r[y];
    }
    return 0;
}
int main() {
    scanf("%d",&T);
    while (T--) {
        bool flag=1;
        scanf("%d%d",&n,&m);
        for (int i=0;i<=n;i++) fa[i]=i,r[i]=0;
        while (m--) {
            int x,y,w;
            scanf("%d%d%d",&x,&y,&w);
            x--;
            if (Union(x,y,w)) {flag=0;break;}
        }
        if (flag) printf("true\n");
        else printf("false\n");
    }
    return 0;
}