From 047e975f977ac4a6356849dc527b6071c4f26f01 Mon Sep 17 00:00:00 2001
From: AnubhutiPuppalwar <puppalwar.anubhuti23@gmail.com>
Date: Wed, 29 Jan 2025 18:32:20 -0800
Subject: [PATCH] Done PreCourse-2

---
 Exercise_1.java | 20 +++++++++++++++--
 Exercise_2.java | 37 +++++++++++++++++++++++++++++---
 Exercise_3.java | 16 ++++++++++++++
 Exercise_4.java | 44 ++++++++++++++++++++++++++++++++++++--
 Exercise_5.java | 57 +++++++++++++++++++++++++++++++++++++++++++++----
 5 files changed, 163 insertions(+), 11 deletions(-)

diff --git a/Exercise_1.java b/Exercise_1.java
index c3ff1141..97c3b94f 100644
--- a/Exercise_1.java
+++ b/Exercise_1.java
@@ -1,8 +1,24 @@
+// Time Complexity : O(logn)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
+//prune the left side if x>arr[mid] else prune the right side.
 class BinarySearch { 
     // Returns index of x if it is present in arr[l.. r], else return -1 
     int binarySearch(int arr[], int l, int r, int x) 
     { 
-        //Write your code here
+        while(l<=r) {
+            int mid=l+(r-l)/2;
+            if(arr[mid]==x) {
+        	return mid;
+            }else if(x>arr[mid]) {
+        	l=mid+1;
+            }else {
+        	r=mid-1;
+            }
+        }
+        return -1;
     } 
   
     // Driver method to test above 
@@ -11,7 +27,7 @@ public static void main(String args[])
         BinarySearch ob = new BinarySearch(); 
         int arr[] = { 2, 3, 4, 10, 40 }; 
         int n = arr.length; 
-        int x = 10; 
+        int x = 40; 
         int result = ob.binarySearch(arr, 0, n - 1, x); 
         if (result == -1) 
             System.out.println("Element not present"); 
diff --git a/Exercise_2.java b/Exercise_2.java
index d0b5fa5f..6a3c246c 100644
--- a/Exercise_2.java
+++ b/Exercise_2.java
@@ -1,3 +1,9 @@
+// Time Complexity : O(nlogn)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
+
 class QuickSort 
 { 
     /* This function takes last element as pivot, 
@@ -7,12 +13,31 @@ class QuickSort
        pivot and all greater elements to right 
        of pivot */
     void swap(int arr[],int i,int j){
-        //Your code here   
+        int t=arr[i];
+        arr[i]=arr[j];
+        arr[j]=t;
     }
     
     int partition(int arr[], int low, int high) 
     { 
-   	//Write code here for Partition and Swap 
+   	int pivot=arr[low];
+   	int i=low+1;
+   	int j=high;
+   	while(i<j) {
+   	    while(i<=high && arr[i]<=pivot) {
+   		i++;
+   	    }
+   	    while(j>=low && arr[j]>=pivot) {
+   		j--;
+   	    }
+   	    if(i<j) {
+   		swap(arr,i,j);
+   	    }
+   	    
+   	}
+   	swap(arr,low,j);
+   	return j;
+	
     } 
     /* The main function that implements QuickSort() 
       arr[] --> Array to be sorted, 
@@ -21,7 +46,13 @@ int partition(int arr[], int low, int high)
     void sort(int arr[], int low, int high) 
     {  
             // Recursively sort elements before 
-            // partition and after partition 
+            // partition and after partition
+	if(low<high) {
+	    int p=partition(arr,low,high);
+	    sort(arr,low,p-1);
+	    sort(arr,p+1,high);
+	}
+	
     } 
   
     /* A utility function to print array of size n */
diff --git a/Exercise_3.java b/Exercise_3.java
index 1f9b752a..1a936435 100644
--- a/Exercise_3.java
+++ b/Exercise_3.java
@@ -1,3 +1,8 @@
+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
 class LinkedList 
 { 
     Node head; // head of linked list 
@@ -20,6 +25,17 @@ void printMiddle()
     { 
         //Write your code here
 	//Implement using Fast and slow pointers
+	if(head==null) {
+	    System.out.println("middle element does not exist");
+	    return;
+	}
+	Node p=head;
+	Node q=head.next;
+	while(q!=null && q.next!=null) {
+	    p=p.next;
+	    q=q.next.next;
+	}
+	System.out.println("middle element is "+p.data);
     } 
   
     public void push(int new_data) 
diff --git a/Exercise_4.java b/Exercise_4.java
index 81afd3c2..a0c5b126 100644
--- a/Exercise_4.java
+++ b/Exercise_4.java
@@ -1,3 +1,8 @@
+// Time Complexity : O(nlogn)
+// Space Complexity : O(n)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
 class MergeSort 
 { 
     // Merges two subarrays of arr[]. 
@@ -5,7 +10,36 @@ class MergeSort
     // Second subarray is arr[m+1..r] 
     void merge(int arr[], int l, int m, int r) 
     {  
-       //Your code here  
+	int n=r-l+1;
+          int[] newarr=new int[n];
+          int p=l;
+          int q=m+1;
+          int i=0;
+          while(i<n && p<=m && q<=r) {
+        	  if(arr[p]<=arr[q]) {
+        	      newarr[i]=arr[p];
+        	      p++;
+        	  }else {
+        	      newarr[i]=arr[q];
+        	      q++;
+        	  }
+        	  i++;
+          }
+          while(p<=m) {
+             newarr[i]=arr[p];
+             i++;
+             p++;
+          }
+          while(q<=r) {
+              newarr[i]=arr[q];
+              i++;
+              q++;
+           }
+          int start=l;
+          for(int j=0;j<n;j++) {
+              arr[start]=newarr[j];
+              start++;
+          }
     } 
   
     // Main function that sorts arr[l..r] using 
@@ -14,6 +48,12 @@ void sort(int arr[], int l, int r)
     { 
 	//Write your code here
         //Call mergeSort from here 
+	if(l<r) {
+	    int mid=l+(r-l)/2;
+	    sort(arr,l,mid);
+	    sort(arr,mid+1,r);
+	    merge(arr,l,mid,r);
+	}
     } 
   
     /* A utility function to print array of size n */
@@ -28,7 +68,7 @@ static void printArray(int arr[])
     // Driver method 
     public static void main(String args[]) 
     { 
-        int arr[] = {12, 11, 13, 5, 6, 7}; 
+        int arr[] = {12, 11, 14, 13, 2, 14}; 
   
         System.out.println("Given Array"); 
         printArray(arr); 
diff --git a/Exercise_5.java b/Exercise_5.java
index 30e82675..a77d2767 100644
--- a/Exercise_5.java
+++ b/Exercise_5.java
@@ -1,20 +1,69 @@
+import java.util.ArrayList;
+import java.util.List;
+
+// Time Complexity : O(nlogn)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : Yes
+// Any problem you faced while coding this : No
+
 class IterativeQuickSort { 
     void swap(int arr[], int i, int j) 
     { 
-	//Try swapping without extra variable 
+	int t=arr[i];
+	arr[i]=arr[j];
+	arr[j]=t;
     } 
   
     /* This function is same in both iterative and 
        recursive*/
     int partition(int arr[], int l, int h) 
     { 
-        //Compare elements and swap.
+	int pivot=arr[l];
+   	int i=l+1;
+   	int j=h;
+   	while(i<j) {
+   	    while(i<=h && arr[i]<=pivot) {
+   		i++;
+   	    }
+   	    while(j>=l && arr[j]>=pivot) {
+   		j--;
+   	    }
+   	    if(i<j) {
+   		swap(arr,i,j);
+   	    }
+   	    
+   	}
+   	swap(arr,l,j);
+   	return j;
     } 
   
     // Sorts arr[l..h] using iterative QuickSort 
-    void QuickSort(int arr[], int l, int h) 
+    void QuickSort(int arr[], int low, int high) 
     { 
-        //Try using Stack Data Structure to remove recursion.
+	Stack<List<Integer>> stk=new Stack();
+        List<Integer> p=new ArrayList<>();
+        p.add(low);
+        p.add(high);
+        stk.push(p);
+        while(!stk.isEmpty()) {
+     	   int x=stk.peek().get(0);
+     	   int y=stk.peek().get(1);
+     	   stk.pop();
+     	   int pivot=partition(arr,x,y);
+            if(pivot-1>x) {
+         	   List<Integer> l1=new ArrayList<>();
+         	   l1.add(x);
+         	   l1.add(pivot-1);
+         	   stk.push(l1);
+            }
+            if(pivot+1<y) {
+         	   List<Integer> l2=new ArrayList<>();
+         	   l2.add(pivot+1);
+         	   l2.add(y);
+         	   stk.push(l2);
+            }
+        }
+        
     } 
   
     // A utility function to print contents of arr