斜率优化

# include <stdio.h>

# include <stdlib.h>

# include <iostream>

# include <string.h>

# include <algorithm>

# define IL inline

# define RG register

# define Fill(a, b) memset(a, b, sizeof(a))

using namespace std;

typedef long long ll;

IL ll Read(){

    RG char c = getchar(); RG ll x = 0, z = 1;

    for(; c > '9' || c < '0'; c = getchar()) z = c == '-' ? -1 : 1;;

    for(; c >= '0' && c <= '9'; c = getchar()) x = (x << 1) + (x << 3) + c - '0';

    return x * z;

}

const int MAXN(50010);

const ll INF(1e18);

int n, len[MAXN], wid[MAXN], id[MAXN], land[MAXN], cnt, Q[MAXN], tail, head;

ll f[MAXN];

IL bool Cmp(RG int a, RG int b){

    return len[a] < len[b] || (len[a] == len[b] && wid[a] < wid[b]);

}

IL double Calc(RG int i, RG int j){

    return 1.0 * (f[j] - f[i]) / (wid[land[i + 1]] - wid[land[j + 1]]);

}

int main(){

    n = Read();

    for(RG int i = 1; i <= n; i++)

        len[i] = Read(), wid[i] = Read(), id[i] = i;

    sort(id + 1, id + n + 1, Cmp);

    for(RG int i = 1; i <= n; i++){

        while(cnt && wid[land[cnt]] <= wid[id[i]]) cnt--;

        land[++cnt] = id[i];

    }

    //鍦熷湴鐨刲ength渚濇閫掑锛屽湡鍦扮殑width渚濇閫掑噺

    for(RG int i = 1; i <= cnt; i++){

        while(head < tail && Calc(Q[head], Q[head + 1]) < len[land[i]]) head++;

        f[i] = f[Q[head]] + 1LL * len[land[i]] * wid[land[Q[head] + 1]];

        while(head < tail && Calc(Q[tail - 1], Q[tail]) >= Calc(Q[tail], i)) tail--;

        Q[++tail] = i;

    }

    printf("%lld\n", f[cnt]);

    return 0;

}