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K_Smallest.cs
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K_Smallest.cs
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using System;
using System.Collections.Generic;
public class Smallest{
public int SmallestIndex(int[] A){
int N = A.Length;
int f=0;
for(int i=1; i<N; i++){
if(A[i]<A[f])
f = i;
}
return f;
}
public IEnumerable<int> TwoSmallestIndex(int[] A){
int N = A.Length;
var res = new List<int>();
int f=0,s=1;
if(A[f] > A[s]){
f = 1; s = 0;
}
for(int i=2; i<N; i++){
if(A[i]<A[f]){
s = f; f = i;
} else if(A[i]<A[s]){
s = i;
}
}
res.Add(f); res.Add(s);
return res;
}
public IEnumerable<int> KSE_Bubble(int[] A, int K){
//bubble sort k times
int N = A.Length;
for(int i=0; i<K; i++){
for(int j=N-1; j>0; j--){
int temp;
if(A[j-1]>A[j]){
temp = A[j];
A[j]=A[j-1];
A[j-1] = temp;
}
}
}
for(int i=0; i<K; i++)
yield return A[i];
}
public IEnumerable<int> KSE_Selection(int[] A, int K){
int N = A.Length;
for(int i=0; i<K; i++){
int pos = i;
for(int j=i+1; j<N; j++){
if(A[pos]>A[j]) pos = j;
}
if(pos != i) {
int temp = A[pos];
A[i] = A[pos];
A[pos] = temp;
}
}
for(int i=0; i<K; i++)
yield return A[i];
}
public IEnumerable<int> KSE_Sorting_Quick(int[] A, int K){
//quick sort
// find a pivot and move smaller before and larger to later
QSort(A);
for(int i=0; i<K; i++)
yield return A[i];
}
internal void QSort(int[] A){
QSort(A, 0, A.Length-1);
}
private void QSort(int[] A, int lo, int hi) {
if(hi<=lo) return;
int p = Partition(A, lo, hi);
QSort(A, lo, p-1);
QSort(A, p+1, hi);
}
private int Partition(int[] A, int lo, int hi){
int v = A[lo]; // 3 1 2 4 5 6
int i=lo, j=hi+1;
while(true){
while(A[++i]<v)
if(i==hi) break;
while(A[--j]>v)
if(j==lo) break;
if(i>=j) break;
Swap(A, i, j);
}
Swap(A, lo, j);
return j;
}
private void Swap(int[] a, int i, int j){
int temp = a[i]; a[i] = a[j]; a[j] = temp;
}
public IEnumerable<int> KSE_MaxHeap(int[] A, int K){
var pq = new MaxPQ(A);
for(int i=0; i<K; i++)
yield return pq.DelMax();
}
public IEnumerable<int> KSE_MinHeap(int[] A, int K){
var heap = new int[K];
for(int i=0; i<heap.Length; i++)
heap[i] = A[i];
var pq = new MinPQ(heap);
for(int i=K; i<A.Length; i++)
pq.InsertAtTop(A[i]);
foreach(var i in pq.PQ())
yield return i;
}
public static void Test(){
int[] a = { 23, 12, 9, 30, 2, 1, 50};
Smallest s = new Smallest();
// Out(s.SmallestIndex(a));
// Out("\n");
// foreach(var i in s.TwoSmallestIndex(a))
// Out(i+" ");
// Out("\n");
// foreach(var i in s.KSE_Bubble(a,3))
// Out(i+" ");
// Out("\n");
// foreach(var i in s.KSE_Selection(a,3))
// Out(i+" ");
// Out("\n");
// foreach(var i in s.KSE_Sorting_Quick(a,3))
// Out(i+" ");
//MaxPQ.Test();
// foreach(var i in s.KSE_MaxHeap(a, 3))
// Out(i+" ");
//MinPQ.Test();
foreach(var i in s.KSE_MinHeap(a,3))
Out(i+" ");
}
private static void OutL(object o){
Console.WriteLine(o);
}
private static void Out(object o){
Console.Write(o);
}
public class MinPQ{
public MinPQ(int[] a){
N = a.Length;
pq = new int[N+1];
for(int i=0; i<N; i++)
pq[i+1] = a[i];
for(int k=N/2; k>0; k--)
Sink(k);
}
public void InsertAtTop(int v){
pq[1] = v;
Sink(1);
}
public int Peek(){return pq[1]; }
private void Sink(int k){
while(2*k <= N ){
int j = 2*k;
if(j<N && pq[j]>pq[j+1]) j++;
if(pq[k]<pq[j]) break;
Swap(k,j);
k = j;
}
}
private void Swim(int k){
while(k>0 && pq[k]<pq[k/2]){
Swap(k, k/2); k = k/2;
}
}
private void Swap(int i, int j){
int temp = pq[i];
pq[i] = pq[j];
pq[j] = temp;
}
public IEnumerable<int> PQ(){ return pq; }
public static void Test(){
var a = new int[] { 23, 12, 9, 30, 2, 1, 50 };
MinPQ pq = new MinPQ(a);
foreach(var i in pq.PQ()){
Out(i+" ");
}
}
private int[] pq;
private int N;
}
public class MaxPQ {
public MaxPQ(int[] H){
N = H.Length;
pq = new int[N+1]; //note pq is 1 larger than that needed capacity
for(int i=0; i<N; i++)
pq[i+1] = H[i];
for(int k=N/2; k>0; k--)
Sink(k);
}
public bool IsEmpty() { return N == 0; }
internal int DelMax(){
int max = pq[1];
Swap(1, N--);
Sink(1);
return max;
}
private void Sink(int k){
while(2*k <= N){
int j = 2*k;
if(j<N && pq[j]<pq[j+1]) j++;
if(pq[j] < pq[k]) break;
Swap(j,k);
k=j;
}
}
private void Swim(int k){
while(k>1 && pq[k/2]<pq[k]){
Swap(k, k/2);
k = k/2;
}
}
private void Swap(int i, int j){
int temp = pq[i];
pq[i] = pq[j];
pq[j] = temp;
}
public int[] pq;
private int N;
public static void Test(){
int[] a = { 23, 12, 9, 30, 2, 1, 50 };
var mpq = new MaxPQ(a);
for(int i=1; i<mpq.pq.Length; i++)
Out(mpq.pq[i]+" ");
}
}
}