zoj2132-The Most Frequent Number

http://acm.zju.edu.cn/onlinejudge/showProblem.do?problemCode=2132

The Most Frequent Number

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Time Limit: 5 Seconds       Memory Limit: 1024 KB

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Seven (actually six) problems may be somewhat few for a contest. But I am really unable to devise another problem related to Fantasy Game Series. So I make up an very easy problem as the closing problem for this contest.

Given a sequence of numbers A, for a number X if it has the most instances (elements of the same value as X) in A, then X is called one of the most frequent numbers of A. Now a sequence of numbers A of length L is given, and it is assumed that there is a number X which has more than L / 2 instances in A. Apparently X is the only one most frequent number of A. Could you find out X with a very limited memory?

Input

Input contains multiple test cases. Each test case there is one line, which starts with a number L (1 <= L <= 250000), followed by L numbers (-2^31 ~ 2^31-1). Adjacent numbers is separated by a blank space.

Output

There is one line for each test case, which is the only one most frequent number X.

Sample Input

5 2 1 2 3 2

8 3 3 4 4 4 4 3 4

Sample Output

2

4

思路：题意很简单，求一个数列里出现次数最多的那个数字，这个数字的个数是大于数列长度的1/2的。这里采用O(1)算法，利用大于1/2这个条件。

 1 #include <cstdio>

 2 

 3 int main()

 4 {

 5     int n,ans;

 6     while(~scanf("%d",&n))

 7     {

 8         int m,cnt=0;

 9         for(int i=0;i<n;i++)

10         {

11             scanf("%d",&m);

12             if(cnt==0)  ans=m,cnt++;

13             else if(ans==m) cnt++;

14             else    cnt--;

15         }

16         printf("%d\n",ans);

17     }

18     return 0;

19 }

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