IOI'96 - Day 2
Sorting is one of the most frequently performed computational tasks. Consider the special sorting problem in which the records to be sorted have at most three different key values. This happens for instance when we sort medalists of a competition according to medal value, that is, gold medalists come first, followed by silver, and bronze medalists come last.
In this task the possible key values are the integers 1, 2 and 3. The required sorting order is non-decreasing. However, sorting has to be accomplished by a sequence of exchange operations. An exchange operation, defined by two position numbers p and q, exchanges the elements in positions p and q.
You are given a sequence of key values. Write a program that computes the minimal number of exchange operations that are necessary to make the sequence sorted.
PROGRAM NAME: sort3
INPUT FORMAT
Line 1: | N (1 <= N <= 1000), the number of records to be sorted |
Lines 2-N+1: | A single integer from the set {1, 2, 3} |
SAMPLE INPUT (file sort3.in)
9 2 2 1 3 3 3 2 3 1
OUTPUT FORMAT
A single line containing the number of exchanges requiredSAMPLE OUTPUT (file sort3.out)
4
剛開始以爲是選擇排序 WA了
先把3放在它應該在的位置 並且交換的時候保證1在2的前面 同樣再把2換到它該在的位置
/*
ID: your_id_here
PROG: sort3
LANG: C++
*/
#include <iostream>
#include<cstdio>
#include<cstring>
#include<stdlib.h>
#include<algorithm>
using namespace std;
int nu[1010],y[1010];
int main()
{
freopen("sort3.in","r",stdin);
freopen("sort3.out","w",stdout);
int i,j,k,n,s=0,x[5]={0},g=1,t;
cin>>n;
for(i = 1; i <= n ; i++)
{
cin>>nu[i];
x[nu[i]]++;
}
x[2]+=x[1];
x[3]+=x[2];
for(i = 1; i <= x[2] ; i++)
{
if(nu[i]==3)
{
s++;
k = i;
for(j = x[2]+1 ; j <= x[3] ; j++)
if(nu[j]==1)
{
k = j;
break;
}
if(k==i)
{
for(j = x[2]+1 ; j <= x[3] ; j++)
if(nu[j]==2)
{
k = j;
break;
}
}
t = nu[i];
nu[i] = nu[k];
nu[k] = t;
}
}
for(i = 1; i <= x[1] ; i++)
{
if(nu[i]==2)
s++;
}
cout<<s<<endl;
fclose(stdin);
fclose(stdout);
return 0;
}