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Cod sursa(job #381377)
#include<stdio.h>
#include<time.h>
#include<stdlib.h>
int v[3000010],i,p,u,k,n,m;
void swap(int &a,int &b){
int aux = a;
a = b;
b = aux;
}
int part(int v[],int li,int lf){
int s=li-1,i,p ;
if(lf- li != 1)
p = li + (rand()%(lf - (li + 1)));
else
p = li + rand()%2;
p = v[p];
for( i = li; i <= lf ; i++)
if(v[i] < p){
s ++;
if(s < i )
swap(v[s],v[i]);
}
return s+1;
}
int main(){
freopen("sdo.in","r",stdin);
freopen("sdo.out","w",stdout);
scanf("%d %d",&n,&k);
for(i = 1; i <= n ; i++)
scanf("%d",&v[i]);
srand(time(0));
p = 1; u = n;
while(true){
m = part(v,p,u);
if(m == k){printf("%d",v[k]);return 0;}
else
if(m > k){u = m - 1;}
else
p = m + 1;
}
return 0;}