愤怒的牛&数列分段II

#include<iostream>
#include<cstdio>
#include<algorithm>
using namespace std;
const int maxn=1e5+7;
int n,m;
int l,r,mid;
int xx[maxn];
bool check(int u){
    int cnt=1;int lft=xx[1]+u;
    for(int i=2;i<=n;i++){
        if(lft<=xx[i]) {cnt++;lft=xx[i]+u;}
    }
    return cnt>=m;
}
int main(){
    cin>>n>>m;
    for(int i=1;i<=n;i++) cin>>xx[i];
    sort(xx+1,xx+n+1);
    l=0;r=xx[n]-xx[1];
    while(l<=r){
        mid=(l+r)/2;
        if(check(mid)) l=mid+1;
        else r=mid-1; 
    }
    cout<<r<<endl;
    return 0;
}

如果不是l=mid+1,r=mid-1的话，因为这里都是整数，很可能出现l=mid的情况，这是就会无限循环下去

数列分段II

#include<iostream>
#include<cstdio>
using namespace std;
typedef long long ll;
const ll maxn=1e6+7;
ll n,m,l,r,mid;
ll a[maxn];
bool check(ll x){
    ll cnt=1;ll lft=a[1];
    for(ll i=2;i<=n;i++){
        if(lft+a[i]>x){cnt++;lft=a[i];}
        else{lft+=a[i];}
    }
    return cnt<=m;
}
int main(){
    cin>>n>>m;
    for(ll i=1;i<=n;i++) {cin>>a[i];r+=a[i];l=max(l,a[i]);}
    while(l<=r){
        mid=(l+r)/2;
        if(check(mid)) r=mid-1;
        else l=mid+1;
    }
    cout<<l<<endl;
    return 0;
}

l不能设成0