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Create LinkedListSort.java #2928

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123 changes: 123 additions & 0 deletions src/main/java/com/thealgorithms/divideandconquer/LinkedListSort.java
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package com.thealgorithms.divideandconquer;
import java.util.*;

public class LinkedListSort
{

//Recursive method for Floats, on first run left = 0, right = list.size() - 1
public static void LLSortFloat(LinkedList<Float> list, int left, int right)
{
if(right > left)
{
int middle = left + (right - left)/2; //determines midpoint
LLSortFloat(list, left, middle); //recursive run for left side
LLSortFloat(list, middle + 1, right); //recursive run for right side
sortFloat(list, left, middle, right); //sorts
}
}

private static void sortFloat(LinkedList<Float> list, int left, int mid, int right)
{
//Extracts/copies data from list and splits into two halves
int val1 = mid - left + 1;
int val2 = right - mid;

float[] arrLeft = new float[val1];
float[] arrRight = new float[val2];

for(int i = 0; i < val1; i++)
arrLeft[i] = list.get(left + i);

for(int i = 0; i < val2; i++)
arrRight[i] = list.get(mid + 1 + i);

//finds lowest available value in each list, lowest of the two is put in earliest available position in list
int i1 = 0, i2 = 0, index = left;
while(i1 < val1 && i2 < val2)
{
if(arrLeft[i1] <= arrRight[i2])
{
list.set(index, arrLeft[i1]);
i1++;
}
else
{
list.set(index, arrRight[i2]);
i2++;
}
index++;
}

//Fills remaining spots in list with incomplete half
while(i1 < val1)
{
list.set(index, arrLeft[i1]);
i1++;
index++;
}

while(i2 < val2)
{
list.set(index, arrRight[i2]);
i2++;
index++;
}
}

//Exact same thing as LLSortFloat but with Integer data type instead of Float
public static void LLSortInt(LinkedList<Integer> list, int left, int right)
{
if(right > left)
{
int middle = left + (right - left)/2;
LLSortInt(list, left, middle);
LLSortInt(list, middle + 1, right);
sortInt(list, left, middle, right);
}
}

private static void sortInt(LinkedList<Integer> list, int left, int mid, int right)
{
int val1 = mid - left + 1;
int val2 = right - mid;

int[] arrLeft = new int[val1];
int[] arrRight = new int[val2];

for(int i = 0; i < val1; i++)
arrLeft[i] = list.get(left + i);

for(int i = 0; i < val2; i++)
arrRight[i] = list.get(mid + 1 + i);

int i1 = 0, i2 = 0, index = left;
while(i1 < val1 && i2 < val2)
{
if(arrLeft[i1] <= arrRight[i2])
{
list.set(index, arrLeft[i1]);
i1++;
}
else
{
list.set(index, arrRight[i2]);
i2++;
}
index++;
}

while(i1 < val1)
{
list.set(index, arrLeft[i1]);
i1++;
index++;
}

while(i2 < val2)
{
list.set(index, arrRight[i2]);
i2++;
index++;
}
}
}