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MergeSortInPlace.java
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MergeSortInPlace.java
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package dev.idion.thinking.sorting;
import java.util.Arrays;
public class MergeSortInPlace {
public static void main(String[] args) {
int[] arr = {2, 9, 7, 5, 3, 1, 6, 2};
sort(arr);
System.out.println(Arrays.toString(arr));
}
public static void sort(int[] arr) {
sort(arr, 0, arr.length - 1);
}
private static void sort(int[] arr, int firstIndex, int lastIndex) {
if (firstIndex < lastIndex) {
int midIndex = (firstIndex + lastIndex) / 2;
sort(arr, firstIndex, midIndex);
sort(arr, midIndex + 1, lastIndex);
merge(arr, firstIndex, midIndex, lastIndex);
}
}
private static void merge(int[] arr, int firstIndex, int midIndex, int lastIndex) {
int i = firstIndex;
int j = midIndex + 1;
if (arr[midIndex] <= arr[j]) { // 정렬 되어있으면 바로 리턴
return;
}
while (i <= midIndex && j <= lastIndex) {
if (arr[i] <= arr[j]) {
i++;
} else {
int value = arr[j];
int index = j;
while (index != i) { // 여기서 O(n^2) 이 됨.
arr[index] = arr[index - 1];
index--;
}
arr[i] = value;
// Update all the pointers
i++;
midIndex++;
j++;
}
}
}
}