POJ 2431 Expedition

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<algorithm>
using namespace std;

int n;
struct Point
{
long long x;
long long sum;
}p[100000 + 10];
long long L, P;

bool cmp(const Point&a, const Point&b)
{
return a.x<b.x;
}

int main()
{
while (~scanf("%d", &n))
{
priority_queue<int>q;
for (int i = 1; i <= n; i++) scanf("%lld%lld", &p[i].x, &p[i].sum);
scanf("%lld%lld", &L, &P);
for (int i = 1; i <= n; i++) p[i].x = L - p[i].x;
sort(p + 1, p + 1 + n, cmp);
if (p
.x != L){ p[n + 1].x = L; p[n + 1].sum = 0; n++; }
int ans = 0; long long pre = 0;
for (int i = 1; i <= n; i++)
{
long long dis = p[i].x - pre;
P = P - dis;
if (p[i].x == L&&P >= 0) break;
if (p[i].x == L)
{
while (P < 0 && (!q.empty()))
{
P = P + q.top(); q.pop(); ans++;
}
if (P < 0) ans = -1;
break;
}
else
{
pre = p[i].x;
if (P == 0)
{
q.push(p[i].sum);
P = P + q.top(); q.pop(); ans++;
}
else if (P < 0)
{
while (P < 0 && (!q.empty()))
{
P = P + q.top(); q.pop(); ans++;
}
if (P < 0) { ans = -1; break; }
else if (P == 0)
{
q.push(p[i].sum);
P = P + q.top(); q.pop(); ans++;
}
else if (P>0) q.push(p[i].sum);
}
else q.push(p[i].sum);
}
}
printf("%d\n", ans);
}
return 0;
}