代码如下：

#include <bits/stdc++.h>
#define rep(i, a, b) for (int i = a; i <= b; i++)
#define per(i, b, a) for (int i = b; i >= a; i--)
using namespace std;
using pii = pair<int, int>;
using graph = vector<vector<pii>>;
using ugraph = vector<vector<int>>;
using ll = long long;
constexpr int MAXN = 3E5 + 5;
constexpr ll INF = 1E18;
int q[MAXN];
ll f[MAXN], c[MAXN], t[MAXN];
int binarySearch(int head, int tail, ll tar) {
    if (tail == head) return head;
    int l = head, r = tail - 1;
    int ans = tail;
    while (l <= r) {
        int m = (l + r) / 2;
        int u = q[m + 1], v = q[m];
        if ((f[u] - f[v]) > tar * (c[u] - c[v])) {
            ans = m;
            r = m - 1;
        } else {
            l = m + 1;
        }
    }
    return ans;
}
int main() {
    ios::sync_with_stdio(false), cin.tie(nullptr);
    int n, s;
    cin >> n >> s;
    for (int i = 1; i <= n; i++) {
        cin >> t[i] >> c[i];
        t[i] += t[i - 1], c[i] += c[i - 1];
    }
    int head = 0, tail = -1;
    f[0] = 0, q[++tail] = 0;
    for (int i = 1; i <= n; i++) {
        int p = binarySearch(head, tail, t[i] + s);
        f[i] = f[q[p]] + t[i] * (c[i] - c[q[p]]) + s * (c[n] - c[q[p]]);
        while (head < tail && (f[q[tail]] - f[q[tail - 1]]) * (c[i] - c[q[tail]]) >= (f[i] - f[q[tail]]) * (c[q[tail]] - c[q[tail - 1]])) tail--;
        q[++tail] = i;
    }
    cout << f[n] << endl;
    return 0;
}

这一行：

while (head < tail && (f[q[tail]] - f[q[tail - 1]]) * (c[i] - c[q[tail]]) >= (f[i] - f[q[tail]]) * (c[q[tail]] - c[q[tail - 1]])) tail--;```
把后面的大于等于改成大于就只能拿75分，这是为什么呢？