POJ 2892 Tunnel Warfare(树状数组+二分)

题目链接

二分求上界和下界，树状数组。注意特殊情况。

#include <cstring>
#include <cstdio>
#include <string>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
int p[100001];
int o[100001];
int stack[100001];
int n;
int lowbit(int t)
{
    return t&(-t);
}
void insert(int t,int d)
{
    while(t <= n)
    {
        p[t] += d;
        t += lowbit(t);
    }
}
int getsum(int t)
{
    int sum = 0;
    while(t > 0)
    {
        sum += p[t];
        t -= lowbit(t);
    }
    return sum;
}
int fr(int x)
{
    int str,end,temp,mid;
    str = 1;
    end = n;
    while(str < end)
    {
        mid = (str+end+1)/2;
        temp = getsum(mid);
        if(temp > x)
            end = mid-1;
        else
            str = mid;
    }
    return end;
}
int fl(int x)
{
    int str,end,temp,mid;
    str = 1;
    end = n;
    while(str < end)
    {
        mid = (str+end)/2;
        temp = getsum(mid);
        if(temp < x)
            str = mid+1;
        else
            end = mid;
    }
    return str;
}
int main()
{
    int i,m,top,num,t;
    char ch[12];
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        top = 0;
        for(i = 1;i <= n;i ++)
        {
            p[i] = 0;
            o[i] = 0;
        }
        for(i = 1; i <= m; i ++)
        {
            scanf("%s",ch);
            if(ch[0] == 'R')
            {
                if(top != 0)
                {
                    o[stack[top]] = 0;
                    insert(stack[top--],-1);
                }
            }
            else if(ch[0] == 'D')
            {
                scanf("%d",&num);
                stack[++top] = num;
                if(o[num] == 0)
                {
                    o[num] = 1;
                    insert(num,1);
                }
            }
            else if(ch[0] == 'Q')
            {
                scanf("%d",&num);
                if(o[num])
                    printf("0
");
                else
                {
                    t = getsum(num);
                    if(t == 0)//注意一下
                    printf("%d
",fr(t));
                    else
                    printf("%d
",fr(t)-fl(t));
                }
            }
        }
    }
    return 0;
}