HDU 5178 pairs 二分查找

pairs

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 592    Accepted Submission(s): 236

Problem Description

n points on the X axis, and their coordinates are (x[i],0),(i=0,1,2,…,n−1). He wants to know how many pairs <a,b> that |x[b]−x[a]|≤k.(a<b)

Input

T (about 5), indicating the number of cases.
Each test case begins with two integers n,k(1≤n≤100000,1≤k≤109).
Next n lines contain an integer x[i](−109≤x[i]≤109), means the X coordinates.

Output

<a,b> that |x[b]−x[a]|≤k.

Sample Input

2 5 5 -100 0 100 101 102 5 300 -100 0 100 101 102

Sample Output

3 10

Source

​​BestCoder Round #31​​

#include<iostream>
#include<stdio.h>
#include<algorithm> 
using namespace std;
#define N 100005
int x[N];

int main()
{
  int t,n,k,i,left,right,mid;
  long long ans;
  
//  freopen("text.txt","r",stdin);
  scanf("%d",&t);
  while(t--)
  {
    scanf("%d%d",&n,&k);
    for(i=0;i<n;i++)
      scanf("%d",&x[i]);
    sort(x,x+n);
    ans=0;
    for(i=0;i<n;i++)
    {
      left=i+1;
      right=n-1;
      while(left<=right)
      {
        mid=(left+right)/2;
        if(x[mid]-x[i]>k)
          right=mid-1;
        else
          left=mid+1;
      }
      ans+=right-i;
    }
    printf("%I64d\n",ans);
  }
  return 0;
}