【codevs 2744】养鱼喂妹纸

二分答案+贪心
注意二分边界啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊啊QAQQQQQQQQQQQQQQQQQQQQQ

#include<cstdio>#include<iostream>#define ll long long#define MAXN 100005using namespace std;ll a[MAXN],b1[MAXN],b[MAXN],maxx;int n;bool check(ll mid){    for(int i=1;i<=n;i++) b1[i]=b[i];    for(int i=1;i<n;i++)    {        if(b1[i]==mid) continue;        if(b1[i]<mid) //l<---r        {            ll tmp=mid-b1[i];            ll road=a[i+1]-a[i];            b1[i+1]-=tmp;            b1[i+1]-=road;        }        else        {            ll tmp=b1[i]-mid;            ll road=a[i+1]-a[i];            if(tmp<=road) b1[i]=mid;            else             {                b1[i]=mid;                b1[i+1]+=tmp-road;            }        }    }    return b1[n]>=mid;}int main(){    scanf("%d",&n);    for(int i=1;i<=n;i++)    {        scanf("%d%d",&a[i],&b[i]);        maxx=max(maxx,b[i]);    }    ll l=1,r=maxx,mid;    while(l<=r)    {        mid=(l+r)>>1;        if(check(mid)) l=mid+1;        else r=mid-1;    }    cout<<r<<endl;    return 0;}