POJ--2388 Who's in the Middle

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忘了是POJ的哪到了……问题如下：

Description
FJ is surveying his herd to find the most average cow. He wants to know how much milk this 'median' cow gives: half of the cows give as much or more than the median; half give as much or less.

Given an odd number of cows N (1 <= N < 10,000) and their milk output (1..1,000,000), find the median amount of milk given such that at least half the cows give the same amount of milk or more and at least half give the same or less.

Input
* Line 1: A single integer N

* Lines 2..N+1: Each line contains a single integer that is the milk output of one cow.

Output
* Line 1: A single integer that is the median milk output.

Sample Input
5
2
4
1
3
5

Sample Output
3

Hint
INPUT DETAILS:

Five cows with milk outputs of 1..5

OUTPUT DETAILS:

1 and 2 are below 3; 4 and 5 are above 3.

用快排：

#include <stdio.h>#define MAXLEN100int QSort(int A[],int low,int high,int i){int ltmp=low,htmp=high;A[0]=A[low];while(low<high){while(low<high&&A[high]>A[0])high--;A[low]=A[high];while(low<high&&A[low]<=A[0])low++;A[high]=A[low];}//whileA[low]=A[0];if(low==i)return A[low];else if(low>i)return(QSort(A,1,low-1,i));//在前面找else return(QSort(A,low+1,htmp,i));//在后面找}//QSortvoid main(){int N,n;int low=1,high=0;int A[MAXLEN+1]={0};scanf("%d",&N);n=N/2+1;while(N--)scanf("%d",&A[++high]);//输入数据printf("%d",QSort(A,low,high,n));}//main

很简单，但得细心……比如，VC中，所有变量的声明必须在最前，否则会出现没有声明的提示……还有：while(low<high&&A[high]>A[0])需在while(low<high&&A[low]<=A[0])前，因为前面使用的是A【0】=A【low】，相当于把low空了出来，以便以后插入

也可以使用其他的排序方法，如计数排序：

#include <stdio.h>#define MAXLEN 100void main(){int cows;int i=0,j;int milk[MAXLEN];int med;int count;scanf("%d",&cows);med=cows/2;//为下标while(cows--)scanf("%d",&milk[i++]);//0号要使用.beak时,cows==-1,i为牛数for(cows=i,i=0;i<cows;i++){ //MARK!for(j=0,count=0;j<cows;j++){if(milk[i]>milk[j])count++;}//forif(count==med)break;}//forprintf("%d",milk[i]);}

本打算在MARK处使用while，形如
while(--i){
for()

}

但发现，用while加大了循环的复杂度，且不清晰又不够简洁，于是还是常规的使用了两个for。

计数排序从总体上看，比快排要简洁不少，但是时间复杂度应该没有快排好……所以个人还是认为使用快排比较好~貌似网上有很多acmer使用的是计数。

由于我的程序都只是在VC中运行而没有去在线判断系统运行，所以不知道到底哪种比较好……