「BZOJ1753」[Usaco2005 qua] Who’s in the Middle
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. 输入N个数,输出升序排列后中间那个数.
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
INPUT DETAILS:
Five cows with milk outputs of 1..5
2
4
1
3
5
INPUT DETAILS:
Five cows with milk outputs of 1..5
Sample Output
3
OUTPUT DETAILS:
1 and 2 are below 3; 4 and 5 are above 3.
OUTPUT DETAILS:
1 and 2 are below 3; 4 and 5 are above 3.
题解
排序一下。。。
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#include<iostream> #include<cstdio> #include<cstdlib> #include<algorithm> #include<cstring> #include<cmath> #define inf 0x7fffffff #define ll long long using namespace std; inline ll read() { ll x=0,f=1;char ch=getchar(); while(ch>'9'||ch<'0'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f; } int n; int a[10005]; int main() { n=read(); for(int i=1;i<=n;i++) a[i]=read(); sort(a+1,a+n+1); printf("%d",a[(n+1)>>1]); return 0; } |
但是这样就没有意思了。。。
我们还是用快速选择吧
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#include<iostream> #include<cstdio> #include<cstring> #include<cstdlib> #include<set> #include<ctime> #include<queue> #include<vector> #include<algorithm> #include<map> #define inf 1000000000 #define ll long long using namespace std; int read() { int x=0,f=1;char ch=getchar(); while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();} while(ch>='0'&&ch<='9'){x=x*10+ch-'0';ch=getchar();} return x*f; } int n; int a[10005]; int select(int l,int r,int K) { int head=l,tail=r; int x=a[head]; while(head<tail) { while(a[tail]>x)tail--; swap(a[head],a[tail]); while(a[head]<x)head++; swap(a[head],a[tail]); } if(head-l==K)return a[head]; else if(head-l>K)return select(l,head-1,K); else return select(head+1,r,K-(head-l+1)); } int main() { n=read(); for(int i=1;i<=n;i++)a[i]=read(); printf("%d",select(1,n,n>>1)); return 0; } |
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