繁华模拟赛 旅行者的笔记

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
const int maxn = 100005;
int n,m,cnt,d[maxn],h[maxn];
int main(){
    freopen("note.in","r",stdin);
    freopen("note.out","w",stdout);
    cin>>n>>m;
    for(int i = 1;i <= m;i++){
        scanf("%d%d",&d[i],&h[i]);
    }
    int ans = max(h[m] + n - d[m],h[1] + d[1] - 1);
    int hg,lw,div,mid;
    for(int i = 2;i <= m;i++){
        div = h[i] - h[i-1];
        if(div < 0) div = -div;
        if(div > d[i]-d[i-1]){
            cout<<"IMPOSSIBLE";
            return 0;
        }
        mid = (h[i] + h[i-1] + d[i] - d[i-1]) >> 1;
        ans = max(ans,mid);
    }
    cout<<ans;
    return 0;
}

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<vector>
#include<queue>
#include<map>
#include<set>
#include<stack>
#include<cstdlib>
#include<string>
#include<bitset>
#define INF 200000000
#define N 100005
#define fi first
#define se second
#define debug(x) cout<<#x<<"="<<x<<endl
#define MP(x,y) make_pair(x,y)
using namespace std;
typedef long long LL;
typedef pair<int,int> pii;
int a[N],b[N];
int main()
{
    int n,m,ans=0,flag,t,l,r,mid,x,now,i;
    freopen("note.in","r",stdin);
    freopen("note.out","w",stdout);
    cin>>n>>m;
    for(i=1;i<=m;i++)
    {
        scanf("%d%d",&a[i],&b[i]);
        if(i==1)
            ans=b[i]+a[i]-1;
        else
        {
            t=a[i]-a[i-1];
            x=b[i]-b[i-1];
            if(abs(x)>t)
            {
                printf("IMPOSSIBLE
");
                return 0;
            }
            x=abs(x);
            ans=max(ans,max(b[i],b[i-1]));
            l=0,r=INF;
            now=0;
            while(l<=r)
            {
                mid=(l+r)>>1;
                if(mid+abs(mid-x)<=t)
                    now=mid,l=mid+1;
                else r=mid-1;
            }
            ans=max(ans,min(b[i],b[i-1])+now);
        }
        if(i==m)
            ans=max(ans,b[i]+n-a[i]);
    }
    cout<<ans<<endl;
    return 0;
}
// davidlee1999WTK 2015/
// srO myk Orz
//ios::sync_with_stdio(false);
/*
100 1
10 10
*/