Pre Course 2 Complete

Exercise_1.java

@@ -1,21 +1,42 @@
-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
-    } 
-
-    // Driver method to test above 
-    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 result = ob.binarySearch(arr, 0, n - 1, x); 
-        if (result == -1) 
-            System.out.println("Element not present"); 
+// Time Complexity : O(logn)
+// Space Complexity :O(1)
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this : No, Have implemented this before so it was easy
+
+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) {
+        // Using the ittrative approch instead of recursive
+        int result = -1;
+        if (arr.length == 0) {
+            return -1;
+        }
+        while (l < r) {
+            int mid = (l + r) / 2;
+            if (arr[mid] == x) {
+                result = mid;
+                break;
+            }
+            if (arr[mid] > x) {
+                r = mid - 1;
+            }
+            if (arr[mid] < x) {
+                l = mid + 1;
+            }
+        }
+        return result;
+    }
+
+    // Driver method to test above
+    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 result = ob.binarySearch(arr, 0, n - 1, x);
+        if (result == -1)
+            System.out.println("Element not present");
         else
-            System.out.println("Element found at index " + result); 
-    } 
-} 
+            System.out.println("Element found at index " + result);
+    }
+}

Exercise_2.java

@@ -1,48 +1,75 @@
-class QuickSort 
-{ 
-    /* This function takes last element as pivot, 
-       places the pivot element at its correct 
-       position in sorted array, and places all 
-       smaller (smaller than pivot) to left of 
-       pivot and all greater elements to right 
-       of pivot */
-    void swap(int arr[],int i,int j){
-        //Your code here   
+
+// Time Complexity :O( n log n)
+// Space Complexity :O(log n)
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this : I had trouble warpping my head around partition and recursion but after watch a few videos and reading a few article I was able to write it but i am still not 100% confident on this one 
+
+class QuickSort {
+    /*
+     * This function takes last element as pivot,
+     * places the pivot element at its correct
+     * position in sorted array, and places all
+     * smaller (smaller than pivot) to left of
+     * pivot and all greater elements to right
+     * of pivot
+     */
+    void swap(int arr[], int i, int j) {
+        int temp;
+        temp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = temp;
     }
-
-    int partition(int arr[], int low, int high) 
-    { 
-   	//Write code here for Partition and Swap 
-    } 
-    /* The main function that implements QuickSort() 
-      arr[] --> Array to be sorted, 
-      low  --> Starting index, 
-      high  --> Ending index */
-    void sort(int arr[], int low, int high) 
-    {  
-            // Recursively sort elements before 
-            // partition and after partition 
-    } 
-
+
+    int partition(int arr[], int low, int high) {
+        int pivot = arr[low];
+        int i = low - 1;
+        int j = high + 1;
+        while (i < j) {
+            do {
+                i++;
+            } while (arr[i] < pivot);
+            do {
+                j--;
+            } while (arr[j] > pivot);
+            if (i < j) {
+                swap(arr, i, j);
+            }
+        }
+        swap(arr, low, j);
+        return j;
+    }
+
+    /*
+     * The main function that implements QuickSort()
+     * arr[] --> Array to be sorted,
+     * low --> Starting index,
+     * high --> Ending index
+     */
+    void sort(int arr[], int low, int high) {
+        if (low < high) {
+            int pivot = partition(arr, low, high);
+            sort(arr, low, pivot);
+            sort(arr, (pivot + 1), high);
+        }
+    }
+
     /* A utility function to print array of size n */
-    static void printArray(int arr[]) 
-    { 
-        int n = arr.length; 
-        for (int i=0; i<n; ++i) 
-            System.out.print(arr[i]+" "); 
-        System.out.println(); 
-    } 
-
-    // Driver program 
-    public static void main(String args[]) 
-    { 
-        int arr[] = {10, 7, 8, 9, 1, 5}; 
-        int n = arr.length; 
-
-        QuickSort ob = new QuickSort(); 
-        ob.sort(arr, 0, n-1); 
-
-        System.out.println("sorted array"); 
-        printArray(arr); 
-    } 
-} 
+    static void printArray(int arr[]) {
+        int n = arr.length;
+        for (int i = 0; i < n; ++i)
+            System.out.print(arr[i] + " ");
+        System.out.println();
+    }
+
+    // Driver program
+    public static void main(String args[]) {
+        int arr[] = { 10, 7, 8, 9, 1, 5 };
+        int n = arr.length;
+
+        QuickSort ob = new QuickSort();
+        ob.sort(arr, 0, n - 1);
+
+        System.out.println("sorted array");
+        printArray(arr);
+    }
+}

Exercise_3.java

@@ -1,53 +1,58 @@
-class LinkedList 
-{ 
-    Node head; // head of linked list 
-
+// Time Complexity :O(n)
+// Space Complexity :O(1)
+// Did this code successfully run on Leetcode :
+// Any problem you faced while coding this : i had never implemented fast and slow pointers, once i searched it online it was pretty easy to understand and implement
+
+class LinkedList {
+    Node head; // head of linked list
+
     /* Linked list node */
-    class Node 
-    { 
-        int data; 
-        Node next; 
-        Node(int d) 
-        { 
-            data = d; 
-            next = null; 
-        } 
-    } 
-
+    class Node {
+        int data;
+        Node next;
+
+        Node(int d) {
+            data = d;
+            next = null;
+        }
+    }
+
     /* Function to print middle of linked list */
-   //Complete this function
-    void printMiddle() 
-    { 
-        //Write your code here
-	//Implement using Fast and slow pointers
-    } 
-
-    public void push(int new_data) 
-    { 
-        Node new_node = new Node(new_data); 
-        new_node.next = head; 
-        head = new_node; 
-    } 
-
-    public void printList() 
-    { 
-        Node tnode = head; 
-        while (tnode != null) 
-        { 
-            System.out.print(tnode.data+"->"); 
-            tnode = tnode.next; 
-        } 
-        System.out.println("NULL"); 
-    } 
-
-    public static void main(String [] args) 
-    { 
-        LinkedList llist = new LinkedList(); 
-        for (int i=15; i>0; --i) 
-        { 
-            llist.push(i); 
-            llist.printList(); 
-            llist.printMiddle(); 
-        } 
-    } 
-} 
+    // Complete this function
+    void printMiddle() {
+        Node fast = head;
+        Node slow = head;
+        while (fast != null && fast.next != null) {
+
+            slow = slow.next;
+            fast = fast.next.next;
+        }
+        System.out.println("------------------------------------");
+        System.out.println(slow.data);
+
+    }
+
+    public void push(int new_data) {
+        Node new_node = new Node(new_data);
+        new_node.next = head;
+        head = new_node;
+    }
+
+    public void printList() {
+        Node tnode = head;
+        while (tnode != null) {
+            System.out.print(tnode.data + "->");
+            tnode = tnode.next;
+        }
+        System.out.println("NULL");
+    }
+
+    public static void main(String[] args) {
+        LinkedList llist = new LinkedList();
+        for (int i = 15; i > 0; --i) {
+            llist.push(i);
+            llist.printList();
+            llist.printMiddle();
+        }
+    }
+}