CDE

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-1.java

@@ -0,0 +1,41 @@
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Scanner;
+public class Mult{
+  public static void main(String[] args){
+    Scanner sc = new Scanner(System.in);
+    int first = sc.nextInt();
+    int second = sc.nextInt();
+
+    if(first < 0){
+        first = -first;
+        second = -second;
+    }
+
+    Map<Integer, Integer> columns = new HashMap<Integer, Integer>();
+        columns.put(first, second);
+    int sum = isEven(first)? 0 : second;
+    do{
+      first = halveInt(first);
+      second = doubleInt(second);
+      columns.put(first, second);
+      if(!isEven(first)){
+          sum += second;
+      }
+    }while(first > 1);
+
+    System.out.println(sum);
+  }
+
+  public static int doubleInt(int doubleMe){
+    return doubleMe << 1; //shift left
+  }
+
+  public static int halveInt(int halveMe){
+    return halveMe >>> 1; //shift right
+  }
+
+  public static boolean isEven(int num){
+    return (num & 1) == 0;
+  }
+}

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-2.java

@@ -0,0 +1,51 @@
+/**
+ * This method will use ethiopian styled multiplication.
+ * @param a Any non-negative integer.
+ * @param b Any integer.
+ * @result a multiplied by b
+ */
+public static int ethiopianMultiply(int a, int b) {
+  if(a==0 || b==0) {
+    return 0;
+  }
+  int result = 0;
+  while(a>=1) {
+    if(!isEven(a)) {
+      result+=b;
+    }
+    b = doubleInt(b);
+    a = halveInt(a);
+  }
+  return result;
+}
+
+/**
+ * This method is an improved version that will use
+ * ethiopian styled multiplication, and also
+ * supports negative parameters.
+ * @param a Any integer.
+ * @param b Any integer.
+ * @result a multiplied by b
+ */
+public static int ethiopianMultiplyWithImprovement(int a, int b) {
+  if(a==0 || b==0) {
+    return 0;
+  }
+  if(a<0) {
+    a=-a;
+    b=-b;
+  } else if(b>0 && a>b) {
+    int tmp = a;
+    a = b;
+    b = tmp;
+  }
+  int result = 0;
+  while(a>=1) {
+    if(!isEven(a)) {
+      result+=b;
+    }
+    b = doubleInt(b);
+    a = halveInt(a);
+  }
+  return result;
+}

Task/Ethiopian-multiplication/Java/ethiopian-multiplication-3.java

@@ -0,0 +1,27 @@
+var eth = {
+	
+	halve : function ( n ){  return Math.floor(n/2);  },
+	double: function ( n ){  return 2*n;              },
+	isEven: function ( n ){  return n%2 === 0);       },
+	
+	mult: function ( a , b ){
+		var sum = 0, a = [a], b = [b];
+		
+		while ( a[0] !== 1 ){
+			a.unshift( eth.halve( a[0] ) );
+			b.unshift( eth.double( b[0] ) );
+		}
+		
+		for( var i = a.length - 1; i > 0 ; i -= 1 ){
+			
+			if( !eth.isEven( a[i] ) ){
+				sum += b[i];
+			}
+		}
+		
+		return sum + b[0];
+
+	}
+}
+
+// eth.mult(17,34) returns 578