[ ST表 ] Codeforces875E Delivery Club

二分答案，然后对每个点二分出以当前距离最远能到达的点，判一下前缀 max 就好了。

#include<cstdio>#include<cstring>#include<iostream>#include<algorithm>using namespace std;inline char nc(){    static char buf[100000],*p1=buf,*p2=buf;    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2)?EOF:*p1++;}inline void Read(int& x){    char c=nc();    for(;c<'0'||c>'9';c=nc());    for(x=0;c>='0'&&c<='9';x=(x<<3)+(x<<1)+c-48,c=nc());}#define N 100010#define M 20#define INF 1e9int i,j,k,n,m,p,a[N],l,r,Mid;int s1[N][M],t1[N][M],s2[N][M],t2[N][M],lg2[N];inline int Max(int x,int y){    int k=lg2[y-x+1];    return max(s1[x][k],t1[y][k]);}inline int Min(int x,int y){    int k=lg2[y-x+1];    return min(s2[x][k],t2[y][k]);}inline bool Check(int s){    int mx=0;    for(int i=1;i<=n;i++){        int l=i,r=n;        while(l<=r){            int Mid=l+r>>1;            if(Max(i,Mid)<=a[i]+s&&Min(i,Mid)>=a[i]-s)l=Mid+1;else r=Mid-1;        }        if(i>2&&i>mx)return 0;        mx=max(mx,r);    }    return 1;}int main(){    Read(n);n+=2;    for(i=1;i<=n;i++)Read(a[i]),s1[i][0]=t1[i][0]=s2[i][0]=t2[i][0]=a[i];    for(i=2;i<=n;i++)lg2[i]=lg2[i>>1]+1;    for(j=1;j<=lg2[n];j++)    for(i=1;i<=n;i++){        if(i+(1<<j-1)<=n)s1[i][j]=max(s1[i+(1<<j-1)][j-1],s1[i][j-1]),s2[i][j]=min(s2[i+(1<<j-1)][j-1],s2[i][j-1]);        if(i-(1<<j-1)>=0)t1[i][j]=max(t1[i-(1<<j-1)][j-1],t1[i][j-1]),t2[i][j]=min(t2[i-(1<<j-1)][j-1],t2[i][j-1]);    }    l=abs(a[1]-a[2]);r=INF;    while(l<=r){        Mid=l+r>>1;        if(Check(Mid))r=Mid-1;else l=Mid+1;    }    cout<<l<<endl;    return 0;}