Language: C++

#pragma GCC optimize(3)
#pragma GCC optimize(2)
#include<bits/stdc++.h>
#define ll long long
#define pb emplace_back
#define mkp make_pair
#define rint register int
#define INF ((1 << 30) - 1)
#define FI(n) FastIO::read(n)
#define FO(n) FastIO::write(n)
#define Pair pair < int, int >
#define mst(a,b) memset(a,b,sizeof(a))
#define foR(i, k, j) for(rint i = (k); i >= (j); i--)
#define For(i, k, j) for(rint i = (k); i <= (j); i++)
#define Foe(i, u) for(rint i = lst[u], v = e[i].v; i; i = e[i].nxt, v = e[i].v)
#define IOS ios::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define file(s) freopen(s".in", "r", stdin); freopen(s".out", "w", stdout)
#define ull unsigned ll
const int P = 998244353; //
using namespace std;
inline void ckmax(int &a, int b) {a = max(a, b);}
inline void ckmin(int &a, int b) {a = min(a, b);}
inline void mulmod(int &a, int b) {a = 1ll * a * b % P;}
inline void addmod(int &a, int b) {int t = a + b; a = (t >= P ? t - P : t); }
inline int ksm(int a, int b) {int ans=1; for(;b;b>>=1) {if(b&1) ans=1ll*ans*a%P;a=1ll*a*a%P;}return ans;}
inline int inv(int a) {return ksm(a, P-2);}

inline void printarray(int *a, int n) {For(i, 1, n) fprintf(stderr, "%d ", a[i]); fprintf(stderr, "\n");}
namespace FastIO {
    const int SIZE=1<<16; char buf[SIZE], obuf[SIZE], str[64]; int bi=SIZE, bn=SIZE, opt;
    int read(char *s) {
        while (bn) {for (;bi<bn&&buf[bi]<=' ';bi++);if (bi<bn) break; bn=fread(buf,1,SIZE,stdin),bi=0;}
        int sn=0;while (bn) {for (;bi<bn&&buf[bi]>' ';bi++) s[sn++]=buf[bi];if (bi<bn) break; bn=fread(buf,1,SIZE,stdin),bi=0;}s[sn]=0;return sn;
    }
    bool read(int& x) {if(x)x=0;int bf=0,n=read(str); if(!n) return 0; int i=0; if (str[i]=='-') bf=1,i=1; for(x=0;i<n;i++) x=x*10+str[i]-'0'; if(bf) x=-x; return 1;}
    void write(int x) {
        if(!x) obuf[opt++] = '0'; else {if(x<0) obuf[opt++]='-',x=-x;int sn=0; while(x)str[sn++]=x%10+'0',x/=10;for (int i=sn-1;i>=0;i--) obuf[opt++]=str[i];}
        if (opt>=(SIZE>>1)){fwrite(obuf, 1, opt, stdout); opt=0;}
    }
    void write(char x) {obuf[opt++]=x;if (opt>=(SIZE>>1)){fwrite(obuf, 1, opt, stdout); opt=0;}}
    void Fflush() { if (opt) fwrite(obuf, 1, opt, stdout); opt=0;}
};
const int MAXN = 2e4 + 5;
const int N = MAXN * 13;
int n, ano[MAXN], pos[MAXN][2];
Pair a[MAXN];
#define ls (k << 1)
#define rs (k << 1 | 1)
#define mid ((l + r) >> 1)
vector < int > e[N];
void build(int k, int l, int r) {
	if(l == r) return e[k + 2 * n].pb(ano[l]);
	e[k + 2 * n].pb(ls + 2 * n), e[k + 2 * n].pb(rs + 2 * n); build(ls, l, mid); build(rs, mid+1, r);
}
void add(int k, int l, int r, int id, int ql, int qr) {
	if(ql > qr) return;
	if(l == ql && r == qr) return e[id].pb(k + 2 * n);
	if(qr <= mid) add(ls, l, mid, id, ql, qr);
	else if(mid < ql) add(rs, mid+1, r, id, ql, qr);
	else add(ls, l, mid, id, ql, mid), add(rs, mid+1, r, id, mid+1, qr);
}
#undef mid
int dfn[N], low[N], s[N], top = 0, ins[N], col[N], cnt, ind;
void tarjan(int u) {
	dfn[u] = low[u] = ++ind; s[++top] = u, ins[u] = 1;
	for(auto v : e[u]) {
		if(!dfn[v]) {
			tarjan(v); ckmin(low[u], low[v]);
		} else if(ins[v]) {
			ckmin(low[u], low[v]);
		}
	}
	if(low[u] == dfn[u]) {
		++cnt;
		while(s[top] != u) ins[s[top]] = 0, col[s[top--]] = cnt;
		ins[s[top]] = 0, col[s[top--]] = cnt;
	}
}
bool check(int mid) {
//	cerr << mid << endl;
	ind = 0; cnt = 0; For(i, 1, 12 * n) e[i].clear(), dfn[i] = low[i] = 0; build(1, 1, 2 * n); 
	For(i, 1, 2 * n) {
		int l = lower_bound(a + 1, a + 1 + 2 * n, mkp(a[i].first - mid + 1, -INF)) - a,
		    r = upper_bound(a + 1, a + 1 + 2 * n, mkp(a[i].first + mid - 1, INF)) - a - 1;
		int t1 = ano[i], t2 = i; if(t1 > t2) swap(t1, t2);
		
//		if(mid <= 10) cerr << i << ' ' << l << ' ' << r << ' ' << t1 << ' ' << t2 << endl;
		add(1, 1, 2 * n, i, l, t1 - 1);
		add(1, 1, 2 * n, i, max(l, t1 + 1), min(r, t2 - 1));
		add(1, 1, 2 * n, i, t2 + 1, r);
	}
	For(i, 1, 12 * n) if(!dfn[i]) tarjan(i);
//	if(mid <= 10) {
//		For(i, 1, 12 * n) cerr << col[i] << ' ';
//		cerr << endl;
//		For(i, 1, n) cerr << pos[i][0] << ' ' << pos[i][1] << endl;
//		cerr << endl << endl;
//	}
	For(i, 1, n) if(col[pos[i][0]] == col[pos[i][1]]) return 0;
	return 1;
}
signed main()
{
    #ifndef ONLINE_JUDGE
        file("pro");
    #endif
	FI(n);
	For(i, 1, n) {
		int x, y; FI(x); FI(y);
		a[i*2-1] = mkp(x, i), a[i*2] = mkp(y, i);
	}
	sort(a + 1, a + 1 + n * 2);
	For(i, 1, n * 2) {
		if(!pos[a[i].second][0]) pos[a[i].second][0] = i;
		else pos[a[i].second][1] = i;
	}
//	For(i, 1, n) cerr << pos[i][0] << ' ' << pos[i][1] << endl;
//	cerr << endl << endl;
	For(i, 1, n) ano[pos[i][0]] = pos[i][1], ano[pos[i][1]] = pos[i][0];
	int l = 1, r = 1e9, res = -1;
	while(l <= r) {
//		cerr << l << ' ' << r  << endl;
		int mid = (l + r) >> 1;
		if(check(mid)) {
			res = mid, l = mid + 1;
		} else r = mid - 1;
	}
	cout << res << endl;
    return FastIO::Fflush(), 0;
}
/*
Think twice :
mod ?
INF ?
n = 1 ?
long long ?
Fastio::Fflush() ?
*/


Compiler output:
a.cc: In function 'void printarray(int*, int)':
a.cc:28:44: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   28 | inline void printarray(int *a, int n) {For(i, 1, n) fprintf(stderr, "%d ", a[i]); fprintf(stderr, "\n");}
      |                                            ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc: In function 'void build(int, int, int)':
a.cc:52:42: error: return-statement with a value, in function returning 'void' [-fpermissive]
   52 |         if(l == r) return e[k + 2 * n].pb(ano[l]);
      |                           ~~~~~~~~~~~~~~~^~~~~~~~
a.cc: In function 'void add(int, int, int, int, int, int)':
a.cc:57:47: error: return-statement with a value, in function returning 'void' [-fpermissive]
   57 |         if(l == ql && r == qr) return e[id].pb(k + 2 * n);
      |                                       ~~~~~~~~^~~~~~~~~~~
a.cc: In function 'bool check(int)':
a.cc:81:31: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   81 |         ind = 0; cnt = 0; For(i, 1, 12 * n) e[i].clear(), dfn[i] = low[i] = 0; build(1, 1, 2 * n);
      |                               ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc:82:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   82 |         For(i, 1, 2 * n) {
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc:92:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   92 |         For(i, 1, 12 * n) if(!dfn[i]) tarjan(i);
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc:99:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   99 |         For(i, 1, n) if(col[pos[i][0]] == col[pos[i][1]]) return 0;
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc: In function 'int main()':
a.cc:108:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
  108 |         For(i, 1, n) {
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc:113:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
  113 |         For(i, 1, n * 2) {
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^
a.cc:119:13: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
  119 |         For(i, 1, n) ano[pos[i][0]] = pos[i][1], ano[pos[i][1]] = pos[i][0];
      |             ^
a.cc:14:31: note: in definition of macro 'For'
   14 | #define For(i, k, j) for(rint i = (k); i <= (j); i++)
      |                               ^