610. Number of number pairs, 610 number Pairs

610. Number of number pairs, 610 number Pairs

★★Input file:dec.inOutput file:dec.outSimple comparison
Time Limit: 1 s memory limit: 128 MB

DEIP
The question is a painful thing!
Questions to see more also have Aesthetic Fatigue, so I give up all the familiar A + B Problem, switch to A-B haha!

Well, the question is this: Given a string of numbers and a number C, it is required to calculate the number of all the A-B = C pairs.

(A number pair with the same number in different positions counts different number pairs)
Input Format
The first line contains two non-negative integers N and C, separated by spaces.
The second row contains N integers separated by spaces as the number of strings to be processed.
Output Format
Output a row that represents the number of all number pairs that meet A-B = C.
Sample Input
4 1
1 1 2 3
Sample Output
3
Data Limit
For 90% of data, N <= 2000;
For 100% of data, N <= 200000.
All input data is within the longint range.
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Great map !!!

 1 #include<iostream> 2 #include<cstdio> 3 #include<cstring> 4 #include<cmath> 5 #include<vector> 6 #include<map> 7 #define LL long long  8 using namespace std; 9 LL read(LL & n)10 {11     int flag=0,x=0;char c='/';12     while(c<'0'||c>'9'){c=getchar();if(c=='-')flag=1;}13     while(c>='0'&&c<='9')x=x*10+(c-48),c=getchar();14     if(flag)n=-x;15     else n=x;16 }17 LL n,c,p,ans=0,a[200001];18 map<LL,int>mp;19 int main()20 {21     freopen("dec.in","r",stdin);22     freopen("dec.out","w",stdout);23     read(n);read(c);24     for(int i=1;i<=n;i++)25         read(a[i]),mp[a[i]]++;26     for(int i=1;i<=n;i++)27     {LL now=a[i]-c;ans=ans+mp[now];}    28     cout<<ans;29     return 0;30 }