Algorithms/Java/Searching/QuickSelect.java at main · Kumar-laxmi/Algorithms · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
// Path: Java\Searching\QuickSelect.java
// Java program to kth smallest element using quickSelect Algorithm.
// Time-Complexity: O(N^2), where N is the size of array.

importjava.util.Random;

publicclassQuickSelect {

// Function to swap two elements in the array
privatestaticvoidswap(int[] arr, inta, intb) {
inttemp = arr[a];
arr[a] = arr[b];
arr[b] = temp;
 }

// Partition function to rearrange elements around the pivot
privatestaticintpartition(int[] arr, intleft, intright, intpivotIndex) {
intpivotValue = arr[pivotIndex];
swap(arr, pivotIndex, right); // Move pivot to the end
intstoreIndex = left;

for (inti = left; i < right; i++) {
if (arr[i] < pivotValue) {
swap(arr, i, storeIndex);
storeIndex++;
 }
 }
swap(arr, storeIndex, right); // Move pivot to its final place
returnstoreIndex;
 }

// Quickselect function
privatestaticintquickSelect(int[] arr, intleft, intright, intk) {
if (left == right)
returnarr[left];

intpivotIndex = left + newRandom().nextInt(right - left + 1);
pivotIndex = partition(arr, left, right, pivotIndex);

if (k == pivotIndex)
returnarr[k];
elseif (k < pivotIndex)
returnquickSelect(arr, left, pivotIndex - 1, k);
else
returnquickSelect(arr, pivotIndex + 1, right, k);
 }

publicstaticvoidmain(String[] args) {
int[] arr = {3, 8, 2, 5, 1, 4, 7, 6};
intk = 4; // Find the 4th smallest element

intresult = quickSelect(arr, 0, arr.length - 1, k - 1);
System.out.println("The " + k + "-th smallest element is: " + result);
 }
}