ATcoder Big Array

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), b_i copies of an integer a_i 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≤a_i,b_i≤10⁵
• 1≤K≤b₁…+…b_n
• 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

3 4
1 1
2 2
3 3

Sample Output 1

3

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

Sample Input 2

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

1

思路：用结构体排序讲a先从小到大排一边，然后再挑选出只要b的总合大于K的结构体然后输出就行

#include<bits/stdc++.h>
using namespace std;
const int N = 1e5+10;
struct str
{
	long long p,q;
}a[N];
bool cmp( str x, str y)  //结构体排序按a的值从小到大排
{
	return x.p<y.p;
}
int main()
{
	long long m,n,i;
	cin>>m>>n;
	for(i = 0; i < m; i++){
		cin>>a[i].p>>a[i].q;
	}
	sort(a,a+m,cmp);
	long long sum = 0;
	for(i = 0; i < m; i++){
		sum += a[i].q;
		if(sum >= n){   //挑选出符合条件的然后输出
			cout<<a[i].p<<endl;
			break;
		}
	}
	return 0;
}