AtCoder：Big Array（思维）

C - Big Array

---

Time limit : 2sec / Memory limit : 256MB

Score : 300 points

Problem Statement

There is an empty array. The following N operations will be performed to insert integers into the array. In the i-th operation (1≤i≤N), bi copies of an integer ai are inserted into the array. Find the K-th smallest integer in the array after the N operations. For example, the 4-th smallest integer in the array {1,2,2,3,3,3} is 3.

Constraints

• 1≤N≤105
• 1≤ai,bi≤105
• 1≤K≤b1…+…bn
• All input values are integers.

---

Input

Input is given from Standard Input in the following format:

N K
a1 b1
:  
aN bN

Output

Print the K-th smallest integer in the array after the N operations.

---

Sample Input 1

Copy

3 4
1 1
2 2
3 3

Sample Output 1

Copy

3

The resulting array is the same as the one in the problem statement.

---

Sample Input 2

Copy

10 500000
1 100000
1 100000
1 100000
1 100000
1 100000
100000 100000
100000 100000
100000 100000
100000 100000
100000 100000

Sample Output 2

Copy

1

题意：给出b[i]个a[i]，i属于[1,N]，组成一个数列，问第K小的数是什么。

思路：数据范围不大，怎么做都行，用set练练手。

# include <bits/stdc++.h>
using namespace std;

typedef long long LL;
multiset<pair<LL, LL> >s;
int main()
{
    LL n, k, a, b;
    scanf("%lld%lld",&n,&k);
    while(n--)
    {
        scanf("%lld%lld",&a,&b);
        s.insert(make_pair(a, b));
    }
    LL sum = 0;
    for(auto it = s.begin(); it!=s.end(); ++it)
    {
        sum += it->second;
        if(sum >= k)
            return 0*printf("%d\n",it->first);
    }
    return 0;
}