Added Leetcode problem of finding Duplicate number in an array

JAVA/DataStructures/Arrays/FindingDuplicateNumber.java

@@ -0,0 +1,32 @@
+import java.util.Scanner;
+
+public class FindDuplicate { //{4,3,1,1,2} me [1,4] elements should only be there and since 1 is repeated it is our answer as per answer
+    public static void main(String[] args) {
+        Scanner in = new Scanner(System.in);
+        int n = in.nextInt();//taking input of length of array by the user
+        int[] a = new int[n + 1];//taking input of array
+        for (int i = 0; i < a.length; i++) {
+            a[i] = in.nextInt();
+        }
+        System.out.println(duplicate(a));
+
+      static int duplicate(int[] a) {
+        int i = 0;
+        while (i < a.length) {
+            if (a[i] != i + 1) {
+                int correct = a[i] - 1;
+                if (a[i] != a[correct]) {
+                    int temp = a[correct];
+                    a[correct] = a[i];
+                    a[i] = temp;
+                } else {
+                    return a[i];
+                }
+            } else {
+                i++;
+            }
+        }
+        return -1;
+   }
+}
+