Poj 2892 tunnel warfare (tree array + binary)

Question:

Three operations

D POS destroys the position of the POs so that it is not connected to the surrounding area.

Q: How many villages are connected to pos.

R repairs the recently destroyed villages.

Train of Thought Analysis:

The tree Array records the number of 1 in this interval.

If [s-e] has e-S + 1 1. This interval is connected.

In this way, we can use the binary method to find the maximum number of connections to a specific location.

Here is the second point.

While (L <= r)

{

If (satisfied)

{

Ans = mid;

L = Mid + 1;

}

Else r = mid-1;

}

#include <cstdio>#include <iostream>#include <algorithm>#include <cstring>#define maxn 55555using namespace std;int n,m;int c[maxn];int lowbit(int x){    return (x&(-x));}int sum(int x){    int ret=0;    while(x>0)    {        ret+=c[x];        x-=lowbit(x);    }    return ret;}void add(int x,int d){    while(x<=n)    {        c[x]+=d;        x+=lowbit(x);    }}int top;int stack[maxn];int main(){    while(scanf("%d%d",&n,&m)!=EOF)    {        memset(c,0,sizeof c);        for(int i=1;i<=n;i++)        {            add(i,1);        }        char str[5];        while(m--)        {            scanf("%s",str);            if(str[0]=='D')            {                int pos;                scanf("%d",&pos);               // if(sum(pos)-sum(pos-1)==0)continue;                add(pos,-1);                stack[top++]=pos;            }            else if(str[0]=='R')            {                int pos=stack[--top];                add(pos,1);            }            else            {                int cur,l,r,ans,rs,re;                scanf("%d",&cur);                if(sum(cur)-sum(cur-1)==0)                {                    printf("0\n");                    continue;                }                l=cur;r=n;                while(l<=r)                {                    int mid=(l+r)>>1;                    if(sum(mid)-sum(cur-1)==mid-cur+1)                    {                        ans=mid;                        l=mid+1;                    }                    else r=mid-1;                }                re=ans;                l=1;r=cur;                while(l<=r)                {                    int mid=(l+r)>>1;                    if(sum(cur)-sum(mid-1)==cur-mid+1)                    {                        ans=mid;                        r=mid-1;                    }                    else l=mid+1;                }                rs=ans;               // printf("%d %d\n",re,rs);                printf("%d\n",re-rs+1);            }        }    }    return 0;}