POJ(2761)Feed the dogs (树状数组+离散化+贪心)

#include <iostream>
#include <algorithm>
#include <stdio.h>
#include <string>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <vector>
#include <map>
#include <queue>
#include <stack>
#include <set>
using namespace std ;
const int maxn = 100002;
struct dog{
    int value;
    int id;
    friend bool operator<(const dog &a,const dog &b){
        return a.value<b.value;
    }
}dog[maxn];
int has[maxn];
int dog_value[maxn];

struct feed{
    int l,r,k;
    int id;
    friend bool operator<(const feed &a,const feed &b){
        if(a.l == b.l)
            return a.r<b.r;
        return a.l<b.l;
    }
}feed[maxn/2];

int n,m;
int c[maxn];
int ans[maxn/2];

int lowbit(int x){
    return x&(-x);
}
void update(int id,int val){
    for(int i = id;i < maxn;i += lowbit(i))
        c[i] += val;
}

int find_kth(int k){
    int ans = 0,cnt = 0;
    for(int i = 20;i >= 0;i--){
        ans += (1<<i);
        if(ans >= maxn || cnt + c[ans] >= k)
            ans -= (1<<i);
        else
            cnt += c[ans];
    }
    return ans+1;
}
int main(){
    while(~scanf("%d%d",&n,&m)){
        for(int i = 1;i <= n;i++){
            scanf("%d",&dog[i].value);
            dog[i].id = i;
        }
        sort(dog+1,dog+n+1);
        dog_value[1] = dog[1].value;
        has[dog[1].id] = 1;
        for(int i = 2,j = 1;i <= n;i++){
            if(dog[i].value != dog[i-1].value)
                dog_value[++j] = dog[i].value;
            has[dog[i].id] = j;
        }
        //for(int i = 1;i <= n;i++)
          //  printf("%d %d\n",has[i],dog_value[i]);
        for(int i = 1;i <= m;i++){
            scanf("%d%d%d",&feed[i].l,&feed[i].r,&feed[i].k);
            feed[i].id = i;
        }
        sort(feed+1,feed+m+1);
        //for(int i = 1;i <= m;i++)
          //  printf("%d %d %d\n",feed[i].l,feed[i].r,feed[i].k);
        feed[0].l=1;feed[0].r=0;
        for(int i=1;i<=m;i++){
            for(int j=feed[i-1].l;j<=feed[i-1].r&&j<feed[i].l;j++)
                update(has[j],-1);
            for(int j=feed[i].l<feed[i-1].r+1?feed[i-1].r+1:feed[i].l;j<=feed[i].r;j++)
                update(has[j],1);
            int num=find_kth(feed[i].k);
            ans[feed[i].id]=dog_value[num];
        }
        for(int i = 1;i <= m;i++)
            printf("%d\n",ans[i]);
    }
    return 0;
}