POJ 2785 4 VALUES WHOSE SUM IS 0 【折半枚举】
2015-06-05 23:41
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Description
The SUM problem can be formulated as follows: given four lists A, B, C, D of 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 that all lists have the same size n .
Input
The first line of the input file contains the size of the lists n (this value can be as large as 4000). We then have n lines containing four integer values (with absolute value as large as 228 ) 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 22 42 -16
-41 -27 56 30
-36 53 -37 77
-36 30 -75 -46
26 -38 -10 62
-32 -54 -6 45
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).
折半枚举时间复杂度O(n^2logn)
代码:
The SUM problem can be formulated as follows: given four lists A, B, C, D of 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 that all lists have the same size n .
Input
The first line of the input file contains the size of the lists n (this value can be as large as 4000). We then have n lines containing four integer values (with absolute value as large as 228 ) 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 22 42 -16
-41 -27 56 30
-36 53 -37 77
-36 30 -75 -46
26 -38 -10 62
-32 -54 -6 45
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).
折半枚举时间复杂度O(n^2logn)
代码:
[code]#include <stdio.h> #include <math.h> #include <stdlib.h> #include <algorithm> #include <queue> #include <iostream> #include <set> #include <string.h> #include <functional> using namespace std; int a[4444],b[4444],c[4444],d[4444]; int p [4444 * 4444]; int main() { int n ; while (scanf("%d",&n)!=EOF) { for (int i=0;i<n;i++) scanf ("%d%d%d%d",&a[i],&b[i],&c[i],&d[i]); for (int i=0;i<n;i++) for (int j=0;j<n;j++) { p[i*n+j] = a[i] + b[j] ; } sort (p,p+n*n); long long ans = 0; for (int i=0;i<n;i++) for (int j=0;j<n;j++) { int cd = -1*(c[i] + d[j]); ans += (upper_bound(p,p+n*n ,cd) - lower_bound(p,p+n*n,cd)); } printf("%I64d\n",ans); } return 0; }
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