hdu4325-Flowers-树状数组+离散化

Flowers

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 3687    Accepted Submission(s): 1821

Problem Description

As is known to all, the blooming time and duration varies between different kinds of flowers. Now there is a garden planted full of flowers. The gardener wants to know how many flowers will bloom in the garden in a specific time. But there are too many flowers in the garden, so he wants you to help him.

 

 

Input

The first line contains a single integer t (1 <= t <= 10), the number of test cases.
For each case, the first line contains two integer N and M, where N (1 <= N <= 10^5) is the number of flowers, and M (1 <= M <= 10^5) is the query times. 
In the next N lines, each line contains two integer S_i and T_i (1 <= S_i <= T_i <= 10^9), means i-th flower will be blooming at time [S_i, T_i].
In the next M lines, each line contains an integer T_i, means the time of i-th query.

 

 

Output

For each case, output the case number as shown and then print M lines. Each line contains an integer, meaning the number of blooming flowers.
Sample outputs are available for more details.

 

 

Sample Input

2

1 1

5 10

4

2 3

1 4

4 8

1

4

6

 

 

Sample Output

Case #1:

0

Case #2:

1

2

1

 

题意：有n朵花，每一朵花只会在固定的时间范围内绽放，m次询问，让你求在某个时刻有多少朵花是绽放的。

思路：这题可以看成是树状数组的区间更新，给出每一朵花开放的时间范围，就相当于做一次区间更新，这个范围内的每个点加1，直接使用树状数组区间跟新的模板就好了。

可是这题有个问题，那就是花开放范围的数据极大（1-10^9），无法直接开数组储存每一个点。那怎么办呢，很明显需要用到数据的离散化。

我们可以发现，虽然花开放范围极大，但是总共只有n朵花，n最大是10^5，每一个范围由两个数l，r组成，再加上最多10^5个查询数，也就意味着一组数据最多出现3*（10^5）个不同的数据，数组完全能够存下。而且我们判断花是否在某一时刻开放，只需要知道数与数之间的相对大小，而不需要在意具体数值（某一时刻在 l , r之间，即花是开的），所以，这就满足了离散化的条件。

我们对每一朵花开放的范围进行离散化，也对查询的时刻进行离散化，这样，就不会改变他们的相对大小。然后使用树状数组区间更新+单点查询即可。

离散化的方法：将所有出现的数存入数组，去除重复出现的数，再进行排序，排序后这个数在数组中对应的下标，即为其离散化之后的数值。

 

代码：

#include<iostream>
#include<cstring>
#include<cstdio>
#include<string>
#include<cmath>
#include<algorithm>
#include<stack>
#include<climits>
#include<map>
#include<queue>
#define eps 1e-7
#define ll long long
#define inf 0x3f3f3f3f
#define pi 3.141592653589793238462643383279
using namespace std;
const int MAXN = 3e5 + 21;

int getNum[MAXN],li[MAXN/3],ri[MAXN/3],c[MAXN];

int lowBit(int x)
{
    return x&(-x);
}

void add(int x,int num,int len) //区间更新 
{
    for(int i=x; i<=len; i+=lowBit(i))
    {
        c[i] += num;
    }
}

ll query(int x) //单点查询 
{
    ll ans = 0;
    for(int i=x; i>0; i-=lowBit(i))
    {
        ans += c[i];
    }
    return ans;
}

int bSerach(int num,int len) //找出某个数在数组中的下标，并返回下标+1 
{
    return lower_bound(getNum,getNum+len,num) - getNum + 1;
}

int main()
{
    int t,n,m,cnt = 0;
    cin>>t;
    while(t--)
    {
        memset(c,0,sizeof(c));
        memset(getNum,0,sizeof(getNum));
    
        scanf("%d%d",&n,&m);
        
        int cnt1 = 0;
        
        for(int i=0; i<n; ++i)
        {
            scanf("%d%d",&li[i],&ri[i]);
            getNum[cnt1++] = li[i]; //将花开放范围出现的数据存入数组 
            getNum[cnt1++] = ri[i];
        }
        
        int ques[MAXN/3];
        for(int i=0; i<m; ++i)
        {
            scanf("%d",&ques[i]); 
            getNum[cnt1++] = ques[i]; //将查询出现的数据存入数组 
        }
        
        sort(getNum,getNum+cnt1); //给所有出现的数排序 
        
        int cnt2 = 1;
        for(int i=1; i<cnt1; ++i)
        {
            if(getNum[i] != getNum[i-1]) //去除重复的数 
                getNum[cnt2++] = getNum[i];
        }
        
        
        for(int i=0; i<n; ++i) //树状数组区间更新
        {
            add( bSerach(li[i],cnt2), 1,cnt2);
            add( bSerach(ri[i],cnt2)+1, -1,cnt2);
        }
        
        printf("Case #%d:\n",++cnt);
        for(int i=0; i<m; ++i)
        {
            cout<<query( bSerach(ques[i], cnt2) )<<endl; //树状数组单点查询 
        }
    }
    return 0;
}