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BinarySearch.java

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+public class BinarySearch {
+    public static void search(int arr[],int key,int s,int e){
+        // int s=0;
+        // int e=arr.length-1;
+        int m=(s+e)/2;
+        while(s<=e){
+            if(arr[m]==key){
+                System.out.println("Element found at index = "+ m);
+                break;
+            }
+
+            else if(arr[m]<key){
+                s=m+1;
+            }
+            else{
+                e=m-1;
+            }
+            m=(s+e)/2;
+        }
+    }
+    public static void main(String[] args) {
+        int arr[]={1,2,3,4,5};
+        int key=1;
+        search(arr,key,0,arr.length-1);
+    }
+}

HashMapInJava.java

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+import java.util.*;
+public class HashMapInJava {
+    public static void main(String args[]) {
+        //Creation
+        HashMap<String, Integer> map = new HashMap<>();
+
+        //Insertion
+        map.put("India", 120);
+        map.put("US", 30);
+        map.put("China", 150);
+
+        System.out.println(map);
+
+
+        map.put("China", 180);
+        System.out.println(map);
+
+        //Searching
+        if(map.containsKey("Indonesia")) {
+            System.out.println("key is present in the map");
+        } else {
+            System.out.println("key is not present in the map");
+        }
+
+        System.out.println(map.get("China")); //key exists
+        System.out.println(map.get("Indonesia")); //key doesn't exist
+
+        //Iteration (1)
+        for( Map.Entry<String, Integer> e : map.entrySet()) {
+            System.out.println(e.getKey());
+            System.out.println(e.getValue());
+        }
+
+        //Iteration (2)
+        Set<String> keys = map.keySet();
+        for(String key : keys) {
+            System.out.println(key+ " " + map.get(key));
+        }
+
+        //Removing
+        map.remove("China");
+        System.out.println(map);
+
+
+    }
+
+}

RemoveDuplicates.java

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+import java.util.*;
+public class RemoveDuplicates {
+    public static int[] removeDup(int arr[]){
+        HashSet<Integer> set=new HashSet<>();
+        for(int num:arr){
+            set.add(num);
+        }
+        int unique[]=new int[set.size()];
+        int i=0;
+        for(int num:set){
+            unique[i++]=num;
+        }
+        return unique;
+    }
+    public static void main(String[] args) {
+        int arr[]={4,59,6,6,1,4,59};
+        int unique[]=removeDup(arr);
+        System.out.println(Arrays.toString(unique));
+
+    }
+}

SubArrayZeroSum.java

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+import java.util.*;
+public class SubArrayZeroSum {
+    public static int[] find(int arr[]){
+        Map<Integer,Integer> sumMap=new HashMap<>();
+    }
+    public static void main(String[] args) {
+        int arr[]={4,5,3,-3,2,-2};
+        int final[]=find(arr);
+    }
+}

TwoSum.java

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+import java.util.HashMap;
+import java.util.*;
+
+public class TwoSum {
+
+public static int[] findTwoSum(int[] nums,int target){
+    Map<Integer,Integer> map = new HashMap<>();
+    for(int i=0;i<nums.length;i++){
+        int complement=target-nums[i];
+        if(map.containsKey(complement)){
+            return new int[]{map.get(complement),i};
+        }
+        map.put(nums[i],i);
+    }
+    return new int[]{-1,-1};
+}
+public static void main(String[] args) {
+    int nums[]={4,5,9,8,6,2,1};
+    int target=7;
+    int[] result=findTwoSum(nums, target);
+    if(result[0] != -1 && result[1]!=-1){
+        System.out.println("Two elements are found = "+ nums[result[0]] +" , "+ nums[result[1]]);
+    }
+    else{
+        System.out.println("No such two elements found");
+    }
+}
+}