Language: C++

#include <iostream>
#include <vector>
#include <set>
#include <algorithm>
#include <list>
#include <cstring>
#include <map>
#include <queue>
#include <ctime>
#include <set>
#include <sstream>
#include <unordered_set>
#include <unordered_map>
#include <cmath>

#define pb push_back
#define mp make_pair
#define ll long long
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ull unsigned long long
#define iloop(a,b) for(ll i = a; i < b; ++i)
#define jloop(a,b) for(ll j = a; j < b; ++j)
#define sz(a) int((a).size()) 
#define pb push_back 
#define all(c) (c).begin(),(c).end() 
#define tr(c,i) for(typeofa((c).begin() i = (c).begin(); i != (c).end(); i++) 
#define present(c,x) ((c).find(x) != (c).end()) 
#define cpresent(c,x) (find(all(c),x) != (c).end()) 
#define p(a) cout << a << "\n";
#define p1(a) cout << a << " ";

#define PI 3.141592653589793
#define MOD (ll)(1e9 + 7)

using namespace std;
static struct IO {
	char tmp[1 << 10];
 
	// fast input routines
	char cur;
 
//#define nextChar() (cur = getc_unlocked(stdin))
//#define peekChar() (cur)
	inline char nextChar() { return cur = getc_unlocked(stdin); }
	inline char peekChar() { return cur; }
 
	inline operator bool() { return peekChar(); }
	inline static bool isBlank(char c) { return (c < '-' && c); }
	inline bool skipBlanks() { while (isBlank(nextChar())); return peekChar() != 0; }
 
	inline IO& operator >> (char & c) { c = nextChar(); return *this; }
 
	inline IO& operator >> (char * buf) {
		if (skipBlanks()) {
			if (peekChar()) {
				*(buf++) = peekChar();
				while (!isBlank(nextChar())) *(buf++) = peekChar();
			} *(buf++) = 0; } return *this; }
 
	inline IO& operator >> (string & s) {
		if (skipBlanks()) {	s.clear(); s += peekChar();
			while (!isBlank(nextChar())) s += peekChar(); }
		return *this; }
 
	inline IO& operator >> (double & d) { if ((*this) >> tmp) sscanf(tmp, "%lf", &d); return *this;	}
 
#define defineInFor(intType) \
	inline IO& operator >>(intType & n) { \
		if (skipBlanks()) { \
			int sign = +1; \
			if (peekChar() == '-') { \
				sign = -1; \
				n = nextChar() - '0'; \
			} else \
				n = peekChar() - '0'; \
			while (!isBlank(nextChar())) { \
				n += n + (n << 3) + peekChar() - 48; \
			} \
			n *= sign; \
		} \
		return *this; \
	}
 
defineInFor(int)
defineInFor(unsigned int)
defineInFor(long long)
 
	// fast output routines
 
//#define putChar(c) putc_unlocked((c), stdout)
	inline void putChar(char c) { putc_unlocked(c, stdout); }
	inline IO& operator << (char c) { putChar(c); return *this; }
	inline IO& operator << (const char * s) { while (*s) putChar(*s++); return *this; }
 
	inline IO& operator << (const string & s) { for (int i = 0; i < (int)s.size(); ++i) putChar(s[i]); return *this; }
 
	char * toString(double d) { sprintf(tmp, "%lf%c", d, '\0'); return tmp; }
	inline IO& operator << (double d) { return (*this) << toString(d); }
 
 
#define defineOutFor(intType) \
	inline char * toString(intType n) { \
		char * p = (tmp + 30); \
		if (n) { \
			bool isNeg = 0; \
			if (n < 0) isNeg = 1, n = -n; \
			while (n) \
				*--p = (n % 10) + '0', n /= 10; \
			if (isNeg) *--p = '-'; \
		} else *--p = '0'; \
		return p; \
	} \
	inline IO& operator << (intType n) { return (*this) << toString(n); }
 
defineOutFor(int)
defineOutFor(long long)
 
#define endl ('\n')
#define cout __io__
#define cin __io__
} __io__;
typedef vector<int> vi; 
typedef vector<vi> vvi; 
typedef pair<int,int> ii; 

ll n;
vector<pair<ll, ll> > vec[100000];
vector<ll> dist(100000,LLONG_MAX);
void shortestPath(ll s)
{
	set<pair<ll, ll> > st;
	
	st.insert(mp(0,s));
	dist[s] = 0;
	while(!st.empty())
	{
		pair<ll, ll> p = *(st.begin());
		st.erase(st.begin());
		ll u = p.second;
		for(auto i = vec[u].begin(); i != vec[u].end(); ++i)
		{
			ll v = (*i).first;
			ll weight = (*i).second;
			if(dist[v] > dist[u] + weight)
			{
				if(dist[v] != LLONG_MAX)
				{
					st.erase(st.find(mp(dist[v], v)));
				}
				dist[v] = dist[u] + weight;
				st.insert(mp(dist[v],v));
			}
		}
	}
}
void solve()
{
	cin >> n;
	ll a,b,c;
	iloop(0,n-1)
	{
		cin >> a >> b >> c;
		vec[a].pb(mp(b,c));
		vec[b].pb(mp(a,c));
	}
	ll q,k;
	cin >> q >> k;
	shortestPath(k);
	iloop(0,q)
	{
		cin >> a >> b;
		p(dist[a] + dist[b])
	}
}
int main()
{
	bool testing = false;
	// IOS
	if(testing)
	{
		freopen("test.txt","rt",stdin);
		int start = clock();
		solve();
		int end = clock();
		cout << "time: " << (end - start)/(double)(CLOCKS_PER_SEC)*1000 << " milliseconds\n";
	}
	else
	{
		solve();
	}
} 

Compiler output:
a.cc:128:24: error: 'LLONG_MAX' was not declared in this scope
  128 | vector<ll> dist(100000,LLONG_MAX);
      |                        ^~~~~~~~~
a.cc:15:1: note: 'LLONG_MAX' is defined in header '<climits>'; this is probably fixable by adding '#include <climits>'
   14 | #include <cmath>
  +++ |+#include <climits>
   15 | 
a.cc: In function 'void shortestPath(long long int)':
a.cc:146:47: error: 'LLONG_MAX' was not declared in this scope
  146 |                                 if(dist[v] != LLONG_MAX)
      |                                               ^~~~~~~~~
a.cc:146:47: note: 'LLONG_MAX' is defined in header '<climits>'; this is probably fixable by adding '#include <climits>'