From 864b7d5646babac36579e6195683357635f775a2 Mon Sep 17 00:00:00 2001
From: Mayank Kochar <51817532+Mayankochar@users.noreply.github.com>
Date: Fri, 30 Oct 2020 03:27:28 +0530
Subject: [PATCH] Create QuickSelect.java

This algorithm allows you to find the kth smallest/largest element efficiently.
---
 QuickSelect.java | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 QuickSelect.java

diff --git a/QuickSelect.java b/QuickSelect.java
new file mode 100644
index 0000000..2a6ce6f
--- /dev/null
+++ b/QuickSelect.java
@@ -0,0 +1,38 @@
+class QuickSelect {
+    public void swap(int[] nums, int i, int j) {
+        int temp = nums[i]; 
+        nums[i] = nums[j];
+        nums[j] = temp;
+    }
+    public int partition(int[] nums,int i,int j) {
+        int l = i - 1;
+        Random r = new Random();
+        int p = i + r.nextInt(j - i + 1);
+        swap(nums,p,j);
+        int pivot = nums[j];
+        for(int k=i;k<j;k++) {
+            if(nums[k]<pivot) {
+                l++;
+                swap(nums,k,l);
+            }
+        }
+        swap(nums,l+1,j);
+        return l+1;
+    }
+    public int findKthLargest(int[] nums, int k) {
+        int r = nums.length - 1;
+        k = r - k + 2;
+        int l = 0;
+        while(l<=r) {
+            int p = partition(nums,l,r);
+            if(p==k-1)
+                return nums[p];
+            else if(p<k-1) {
+                l = p + 1;
+            }
+            else
+                r = p - 1;
+        }
+        return -1;
+    }
+}