[BZOJ1637][Usaco2007 Mar]Balanced Lineup

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
char buf[10000000], *ptr = buf - 1;
inline int readint(){
    int f = 1, n = 0;
    char ch = *++ptr;
    while(ch < ‘0‘ || ch > ‘9‘){
        if(ch == ‘-‘) f = -1;
        ch = *++ptr;
    }
    while(ch <= ‘9‘ && ch >= ‘0‘){
        n = (n << 1) + (n << 3) + ch - ‘0‘;
        ch = *++ptr; 
    }
    return f * n;
}
const int maxn = 50000 + 10;
struct Node{
    int id, x;
    Node(){}
    Node(int _id, int _x): id(_id), x(_x){}
    bool operator < (const Node &a) const {
        return x < a.x;
    }
}a[maxn];
int N, l[maxn * 2] = {0};
int main(){
    fread(buf, sizeof(char), sizeof(buf), stdin);
    N = readint();
    for(int i = 1; i <= N; i++){
        a[i].id = readint();
        a[i].x = readint();
    }
    sort(a + 1, a + N + 1); 
    int ans = 0;
    for(int sum = 0, i = 1; i <= N; i++){
        if(a[i].id == 1) sum++;
        else sum--;
        if(sum == 0) ans = max(ans, a[i].x - a[1].x);
        else{
            if(l[sum + N] != 0) ans = max(ans, a[i].x - a[l[sum + N] + 1].x);
            else l[sum + N] = i;
        }
    }
    printf("%d\n", ans);
    return 0;
}