HDU 4217 Data Structure?（树状数组求前k大）

Problem Description

Data structure is one of the basic skills for Computer Science students, which is a particular way of storing and organizing data in a computer so that it can be used efficiently. Today let me introduce a data-structure-like problem for you.
Original, there are N numbers, namely 1, 2, 3...N. Each round, iSea find out the Ki-th smallest number and take it away, your task is reporting him the total sum of the numbers he has taken away.

 

Input

The first line contains a single integer T, indicating the number of test cases.
Each test case includes two integers N, K, K indicates the round numbers. Then a line with K numbers following, indicating in i (1-based) round, iSea take away the Ki-th smallest away.

Technical Specification
1. 1 <= T <= 128
2. 1 <= K <= N <= 262 144
3. 1 <= Ki <= N - i + 1

 

Output

For each test case, output the case number first, then the sum.

 

Sample Input

   
   
   
   

    
    
    
    2
3 2
1 1
10 3
3 9 1
   
   
   
   

 

Sample Output

   
   
   
   

    
    
    
    Case 1: 3
Case 2: 14
   
   
   
   

题意：n个数1-n，k次操作，每次取出第ki小的数。问所有取出数字之和。

思路：树状数组。开始所有位置都是1，如果有数字被去掉就-1。然后在查找第ki小的数字的时候，利用树状数组去进行求和，看数字个数为k时是第几个。

代码：

#include <stdio.h>
#include <string.h>
#include <iostream>
using namespace std;
const int N = 277777;

int t, n, m, bit[N], num, i;
long long ans;

void add(int x, int v) {
	while (x <= n) {
		bit[x] += v;
		x += (x&(-x));
	}
}

int Sum(int k) {
	int num = 0;
	int x = 0;
	for (int i = 18; i >= 0; i--) {
		if (x + (1<<i) <= n && bit[x + (1<<i)] + num < k) {
			x += (1<<i);
			num += bit[x];
		}

	}
	return x + 1;
}

void init() {
	ans = 0;
	memset(bit, 0, sizeof(bit));
	scanf("%d%d", &n, &m);
	for (i = 1; i <= n; i++)
		add(i, 1);
	for (i = 0; i < m; i++) {
		scanf("%d", &num);
		int s = Sum(num);
		ans += s;
		add(s, -1);
	}
}

int main() {
	int cas = 0;
	scanf("%d", &t);
	while (t--) {
		init();
		//printf("Case %d: %lld\n", ++cas, ans);
		cout <<"Case "<<++cas<<": "<<ans<<endl;
	}
	return 0;
}