【Codeforces875E】Delivery Club

首先二分答案，然后从后往前跑目的地维护可存在的区间。区间不存在或者开始点不在最终区间就不行，否则可以。

#include <bits/stdc++.h>#define gc getchar()#define ll long long#define N 100009#define mid (l+r>>1)using namespace std;int n,s,t,a[N];int read(){    int x=1;    char ch;    while (ch=gc,ch<'0'||ch>'9') if (ch=='-') x=-1;    int s=ch-'0';    while (ch=gc,ch>='0'&&ch<='9') s=s*10+ch-'0';    return s*x;}bool check(int x){    if (abs(s-t)>x) return 0;    int l=a[n]-x,r=a[n]+x;    for (int i=n-1;i;i--)    {        int L=a[i]-x,R=a[i]+x;        if (a[i]<l||a[i]>r)        {            L=max(L,l);            R=min(R,r);        }        if (L>R) return 0;        l=L,r=R;    }    return (s>=l&&s<=r||t>=l&&t<=r);}int main(){    n=read(),s=read(),t=read();    for (int i=1;i<=n;i++) a[i]=read();    int l=0,r=1000000000,ret=1000000000;    while (l<=r)    {        if (check(mid)) ret=mid,r=mid-1;        else l=mid+1;    }    printf("%d\n",ret);    return 0;}