#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<cstdio>
using namespace std;
const int MAXN = 1000000;

int f[MAXN*4];
int bri = 0;

struct NUM{
int a, b, c;

}num[MAXN];

bool cmp(NUM u, NUM v){
return u.c > v.c;

}

int find(int x){
if(f[x] != x)
return f[x] = find(f[x]);
return x;
}

int main()
{
int n, m, ans = 0;
scanf("%d%d", &n, &m);
for(int i=1; i<=m; i++)
scanf("%d%d%d", &num[i].a, &num[i].b, &num[i].c);
sort(&num[1], &num[1]+m, cmp);
for(int i=1; i<=n*2; i++)
f[i] = i;
for(int i=1; i<=m; i++){
int bri1 = find(num[i].a) ,bri2 = find(num[i].b);
if(bri1 == bri2){
ans = num[i].c;
break;
}
f[bri1] = find(num[i].b + n);
f[bri2] = find(num[i].a + n);
}
printf("%d", ans);
system("pause");

return 0;

}
水一发（感谢楼下大神）

二分答案+二分图染色
有很多小细节最好调试时注意一下
#include<cstdio>
#include<iostream>
#include<vector>
#include<queue>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<string>
using namespace std;
const int MAX=0x7fffffff,N=100001;
vector<int> to[N],cost[N];
vector<int> link[N];
queue<int> q;
int col[N],a[100005];
int n,m;
int ANS;
void ser(int,int);
bool jud(int);
int main()
{
scanf("%d%d",&n,&m);

for(int i=1;i<=m;i++)
{
int z,b,v;
scanf("%d%d%d",&z,&b,&v);
a[i]=v;
to[z].push_back(b);to[b].push_back(z);
cost[z].push_back(v);cost[b].push_back(v);
}
sort(a+1,a+m+1);
if(jud(0)==true){
cout<<0;
return 0;
}

ser(1,m);

return 0;
}
void ser(int l,int r){
if(r==l){
if(jud(a[l])==true){
cout<<a[l];
return ;
}
else{
cout<<ANS;
return ;
}
}

int midd=(l+r)>>1;
int mid=a[midd];
if(jud(mid)==true){
ANS=mid;
r=midd;
ser(l,r);
}
else{
l=midd+1;
ser(l,r);
}
}
bool jud(int x){
memset(link,0,sizeof(link));
for(int i=1;i<=n;i++){
for(int j=0;j<to[i].size();j++){
int xx=to[i][j];int yy=cost[i][j];
if(yy>x){
link[i].push_back(xx);
}
}
}

memset(col,0,sizeof(col));

for(int k=1;k<=n;k++){
if(col[k]==0){
while(q.size()>0) q.pop();
q.push(k);
while(q.size()>0){
int gg=q.front();
q.pop();
if(col[gg]==0){
col[gg]=1;
}
for(int h=0;h<link[gg].size();h++){
int jj=link[gg][h];
if(col[jj]==0){
col[jj]=-col[gg];
q.push(jj);
}
else{
if(col[jj]==col[gg]){
return false;
}
}

}
}

}

}
return true;
}

二分暴力

program erfentu;
var
ans,maxn,i,l,j,k,n,m,tot,t:longint;
aa:array[0..100000,0..2] of longint;
o,color:array[0..100000] of longint;
a,b,c:array[0..100000] of longint;
vis:array[0..100000] of boolean;
can:boolean;
function max(a,b:longint):longint;
begin
if a>b then exit(b) else exit(a);
end;
procedure addedge(p,q,w:longint);
begin
inc(tot);
aa[tot,1]:=q;
aa[tot,0]:=o[p];
aa[tot,2]:=w;
o[p]:=tot;
end;
procedure init;
begin
fillchar(color,sizeof(color),0);
readln(n,m);
tot:=0;
for i:=1 to m do
begin
read(a[i],b[i],c[i]);
addedge(a[i],b[i],c[i]);
addedge(b[i],a[i],c[i]);
end;
ans:=maxlongint;
fillchar(vis,sizeof(vis),false)
end;
procedure dfs(x:longint);
begin
vis[x]:=true;
t:=aa[x,1];
while (t<>0) do
begin
if vis[o[t]] then
begin
if (color[x]=color[o[x]]) then
begin
can:=false;
ans:=max(ans,aa[x,2]);
end;
end
else
begin
color[o[t]]:=1-color[x];
dfs(o[t]);
end;
t:=aa[t,0];
end;
end;
procedure work;
begin
for i:=1 to n do
begin
if not vis[i] then
begin
color[i]:=0;
dfs(i);
end;
end;
if can then writeln(0)
else writeln(ans);
end;
begin
init;
work;
end.