uploading class code

Author: Algorithmica

2018-feb/adhoc-thinking/src/com/alg/top20/adhoc/TwoSum.java

@@ -0,0 +1,72 @@
+package com.alg.top20.adhoc;
+
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Random;
+
+public class TwoSum {
+
+	public static boolean twoSum1(int[] in, int target) {
+		for (int i = 0; i < in.length; ++i) {
+			for (int j = i + 1; j < in.length; ++j) {
+				if (in[j] == target - in[i])
+					return true;
+			}
+		}
+		return false;
+	}
+
+	// sort + binary search
+	public static boolean twoSum2(int[] in, int target) {
+		Arrays.sort(in);
+		for (int i = 0; i < in.length; ++i) {
+			if (Arrays.binarySearch(in, i + 1, in.length, target - in[i]) >= 0)
+				return true;
+		}
+		return false;
+	}
+
+	// sort + 2-pointer approach
+	public static boolean twoSum3(int[] in, int target) {
+		Arrays.sort(in);
+		int left = 0, right = in.length - 1;
+
+		while (left < right) {
+			if (in[left] + in[right] == target)
+				return true;
+			if (in[left] + in[right] < target)
+				++left;
+			else
+				--right;
+		}
+		return false;
+	}
+	
+	// DS based - hashset
+	public static boolean twoSum4(int[] in, int target) {
+		HashSet<Integer> hset = new HashSet<Integer>();
+		for (int i = 0; i < in.length; ++i) {
+			if (hset.contains(target-in[i]))
+				return true;
+			hset.add(in[i]);
+		}
+		return false;
+	}
+
+	public static void main(String[] args) {
+		int n = Integer.parseInt(args[0]);
+		int[] in = new int[n];
+		//testcase1
+		Random r = new Random();
+		for(int i = 0; i < in.length; ++i)
+			in[i] = r.nextInt(3*n) + 1;
+		int target = 0;
+		//System.out.println(Arrays.toString(in));
+		long start = System.currentTimeMillis();
+		System.out.println(twoSum4(in, target));
+		long end = System.currentTimeMillis();
+		System.out.println("Time:" + (end-start)/1000.0 +"seconds");
+
+	}
+
+}