POJ 2785:4 Values whose Sum is 0 (bidirectional BFS) __ Search

Source: Internet
Author: User
4 Values whose Sum is 0
Time Limit: 15000MS Memory Limit: 228000K
Total submissions: 20020 accepted: 5977
Case Time Limit: 5000MS


Description The SUM problem can be formulated as Follows:given four lists A, B, C, D of an integer values, compute how many Quadruplet (A, B, C, D) ∈a x B x C x D are such that A + B + c + d = 0. In the following, we assume so all lists have the same size n.


Input the the ' the ' input file contains the size of the lists n (this value can as large as 4000). We then have n lines containing four integer values (with absolute value as large as 2) that belong respectively to A, B, C and D.


Output for each input file, your program has to write the number quadruplets whose sum is zero.


Sample Input

6
-45 42-16
-41-27
-36 53-37
-36 30-75-46
26-38-10
45 -32-54-6


Sample Output

5


Hint Sample Explanation:indeed, the sum of the five following quadruplets is zero: (-45,-27, 42, 30), (26, 30,-10,-46) , (-32, 22, 56,-46), (-32, 30,-75, 77), (-32,-54, 56, 30).


To select one of the four groups to meet the number of a+b+c+d==0.


The direct use of BFS time complexity is O (n^4), obviously will time out, we can divide the whole four sets of data into two groups, and then is to two sets of data separately BFS, the final statistical results, so that the complexity of the Times reduced to O (n^2), it is easy to go through the ~


AC Code:

 #include <cstdio> #include <math.h> #include <iostream> #include <algorithm>
#define MAX (A,B) (A>B?A:B) using namespace std;
__int64 a[4005],b[4005],c[4005],d[4005];
__int64 cd[4005*4005];
    int main () {int n;
    scanf ("%d", &n);
    for (int i=0; i<n; i++) scanf ("%i64d%i64d%i64d%i64d", a+i,b+i,c+i,d+i);
    for (int i=0; i<n; i++) for (int j=0; j<n; j + +) Cd[i*n+j]=c[i]+d[j];
    Sort (cd,cd+n*n);
    __int64 ans=0;
            for (int i=0; i<n; i++) for (int j=0; j<n; J + +) {__int64 ab=-(a[i]+b[j));
        Ans+=upper_bound (Cd,cd+n*n,ab)-lower_bound (CD,CD+N*N,AB);
    printf ("%i64d\n", ans);
return 0; }

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.