diff --git a/firstIndexOfNumber.java b/firstIndexOfNumber.java
new file mode 100644
index 0000000..78d00e8
--- /dev/null
+++ b/firstIndexOfNumber.java
@@ -0,0 +1,19 @@
+
+public class firstIndexOfNumber {
+
+	public static int fIndex(int input[], int x) {
+		
+        return fIndex(input,x,0);
+    }
+    public static int fIndex(int input[],int X,int sIndex){
+        if(sIndex > input.length-1){
+            return -1;
+        }
+        if(input[sIndex]==X){
+            return sIndex;
+        }
+        int smallAns = fIndex(input,X,sIndex+1);
+        return smallAns;
+    }
+	
+}
\ No newline at end of file
diff --git a/lastIndexOfNumber.java b/lastIndexOfNumber.java
new file mode 100644
index 0000000..3c24ded
--- /dev/null
+++ b/lastIndexOfNumber.java
@@ -0,0 +1,24 @@
+
+public class lastIndexOfNumber{
+
+	public static int lIndex(int input[], int x) {
+		
+        return lIndex(input,x,0);
+	}
+    public static int lIndex(int input[], int X, int sIndex){
+        if(sIndex > input.length-1){
+            return -1;
+        }
+        
+        int smallAns = lIndex(input,X,sIndex+1);
+        if(smallAns == -1){
+            if(input[sIndex]==X){
+                return sIndex;
+            }else{
+                return -1;
+            }
+        }else{
+            return smallAns;
+        }      
+    }  
+}
\ No newline at end of file
diff --git a/pairSumToZero.java b/pairSumToZero.java
new file mode 100644
index 0000000..8a9ed93
--- /dev/null
+++ b/pairSumToZero.java
@@ -0,0 +1,31 @@
+import java.util.*;
+
+public class Solution {
+	
+    public static int PairSum(int[] input, int size) {
+        HashMap<Integer,Integer> map = new HashMap<>();
+         for(int i=0;i<size;i++){
+            if(map.containsKey(input[i])){
+                map.put(input[i],map.get(input[i])+1);
+            }else{
+                map.put(input[i],1);
+            }
+        }
+        int count =	0;
+        for(int i=0;i<size;i++){
+            if(input[i]  == 0){
+               int k = map.get(0);
+                count += (k*(k-1))/2;
+                map.put(input[i],0);
+                continue;
+            }
+         if(map.containsKey(input[i]) && map.containsKey(-(input[i]))){
+            count += map.get(input[i])*map.get(-(input[i]));
+             map.put(input[i],0);
+             map.put(-(input[i]),0);
+         }
+            
+        }
+        return count;  
+    }
+}
\ No newline at end of file
diff --git a/removeX.java b/removeX.java
new file mode 100644
index 0000000..16d005e
--- /dev/null
+++ b/removeX.java
@@ -0,0 +1,18 @@
+public class solution {
+
+	public static String removeX(String input){
+        return removeX(input,0);
+    }
+
+    public static String removeX(String input , int sIndex){
+        if(sIndex == input.length()){
+            return "";
+        }
+        if(input.charAt(sIndex)=='x'){
+            return removeX(input,sIndex+1);
+        }
+        String ans = input.charAt(sIndex) + removeX(input,sIndex+1);
+        return ans;
+
+	}
+}