Create SingleNumber.java

Author: techieJarek

SingleNumber.java

@@ -0,0 +1,56 @@
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Given a non-empty array of integers, every element appears twice except for one. Find that single one.
+ */
+public class SingleNumber {
+    public static void main(String[] args){
+        int[] nums = {4,1,2,1,2};
+
+        System.out.println("Single number is : " + singleNumber(nums));
+
+        //Improved solution - single pass
+        System.out.println("Single number is : " + singleNumberInSinglePass(nums));
+
+        //Improved solution - Space complexity O(1)
+        System.out.println("Single number is : " + singleNumberXOR(nums));
+
+    }
+
+    public static int singleNumber(int[] nums) {
+        Map<Integer,Integer> map = new HashMap<>();
+        for(int i=0; i < nums.length; i++){
+            if(map.get(nums[i])==null){
+                map.put(nums[i], 1);
+            } else {
+                map.put(nums[i], map.get(nums[i])+1);
+            }
+        }
+
+        for(int key : map.keySet()){
+            if(map.get(key) == 1) return key;
+        }
+
+        return -1;
+    }
+
+    private static int singleNumberInSinglePass(int[] nums) {
+        Map<Integer,Integer> map = new HashMap<>();
+        for(int i=0; i < nums.length; i++){
+            if(map.containsKey(nums[i])) map.remove(nums[i]);
+            else map.put(nums[i], 1);
+        }
+        return map.keySet().iterator().next();
+    }
+
+    public static int singleNumberXOR(int[] nums) {
+        int num = 0;
+        for (int x : nums) {
+            num ^= x;
+            System.out.println(num);
+        }
+        return num;
+    }
+
+}