(HDU - 4334)Trouble
2017-08-24 08:28
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(HDU - 4334)Trouble
Time Limit: 10000/5000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others)Total Submission(s): 6218 Accepted Submission(s): 1738
Problem Description
Hassan is in trouble. His mathematics teacher has given him a very difficult problem called 5-sum. Please help him.The 5-sum problem is defined as follows: Given 5 sets S_1,…,S_5 of n integer numbers each, is there a_1 in S_1,…,a_5 in S_5 such that a_1+…+a_5=0?
Input
First line of input contains a single integer N (1≤N≤50). N test-cases follow. First line of each test-case contains a single integer n (1<=n<=200). 5 lines follow each containing n integer numbers in range [-10^15, 1 0^15]. I-th line denotes set S_i for 1<=i<=5.Output
For each test-case output “Yes” (without quotes) if there are a_1 in S_1,…,a_5 in S_5 such that a_1+…+a_5=0, otherwise output “No”.Sample Input
22
1 -1
1 -1
1 -1
1 -1
1 -1
3
1 2 3
-1 -2 -3
4 5 6
-1 3 2
-4 -10 -1
Sample Output
NoYes
题目大意:在5个集合中分别取一个数使这5个数的和为0。
思路:这题刚开始我想到的是二分,因为这题就是典型的二分,先预处理出前三个集合的和,后两个集合的和,然后二分查找,时间复杂度为O(n3logn)。再看了大佬的思路后,发现了一种更好的方法,先利用分治思想,处理前两个集合的和sum1,3 4集合的和sum2。然后要介绍一种尺取法(也就是一种贪心思想):如何快速判断是否有A[i]+B[j]=x,先将A,B送小到大排序得到有序序列,可以先让i指向A数组的首指针,j指向B数组的为指针,判断A[i]+B[j]与x的大小关系,若A[i]+B[j]>x则j–;若A[i]+B[j]< x则i++。这样就可以在线性时间内判断是否有A[i]+B[j]=x。利用这种方法最后的复杂度为O(n3)。显然选择这种方法更好。
#include<cstdio> #include<algorithm> using namespace std; typedef long long LL; const int maxn=205; LL a[5][maxn]; LL sum1[maxn*maxn],sum2[maxn*maxn]; int main() { int T; scanf("%d",&T); while(T--) { int n; scanf("%d",&n); for(int i=0;i<5;i++) for(int j=0;j<n;j++) scanf("%lld",&a[i][j]); int k=0; for(int i=0;i<n;i++) for(int j=0;j<n;j++) sum1[k++]=a[0][i]+a[1][j]; k=0; for(int i=0;i<n;i++) for(int j=0;j<n;j++) sum2[k++]=a[2][i]+a[3][j]; sort(sum1,sum1+k); sort(sum2,sum2+k); bool flag=false; for(int i=0;i<n&&!flag;i++) { int l=0,r=k-1; while(l<k&&r>=0) { if(sum1[l]+sum2[r]==-a[4][i]) { flag=true; break; } else if(sum1[l]+sum2[r]>-a[4][i]) r--; else l++; } } if(flag) printf("Yes\n"); else printf("No\n"); } return 0; }
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