Done BackTracking

ExpressionAddOperators.java

@@ -0,0 +1,62 @@
+//package Backtracking-1;
+
+import java.util.*;
+
+public class ExpressionAddOperators {
+    List<String> res;
+    private List<String> solution(String num, int target){
+        this.res = new ArrayList<>();
+        helper(num, 0, 0l, 0l, "", target);
+        return res;
+    }
+
+    private void helper(String num, int pivot, long calc , long tail, String path , int target){
+
+        //base 
+        if(pivot == num.length()){
+            if(calc == target) {
+                res.add(path);
+            }
+            return;
+        }
+
+
+        //logic
+        for(int i = pivot; i< num.length();i++){
+            //preceeding 0 
+            if(num.charAt(pivot)=='0' && i>pivot){
+                continue;
+            }
+
+            //what if > 10 digits
+            long cur = Long.parseLong(num.substring(pivot, i+1));
+            if(pivot==0){
+                helper(num, i+1, cur, cur, path+cur, target);
+            }
+            else{
+
+            //recurse
+            //+
+            helper(num, i+1, calc + cur, cur, path + "+" + cur, target);
+
+
+            //-
+            helper(num, i+1, calc - cur, -cur, path + "-" + cur, target);
+
+            //* 
+            helper(num, i+1, calc - tail + tail * cur, tail * cur, path + "*" + cur, target);
+            }
+        }
+    }
+
+    public static void main(String[] args){
+        String num = "123";
+        int target = 6;
+        ExpressionAddOperators solver = new ExpressionAddOperators();
+        List<String> res = solver.solution(num, target);
+        System.out.println("List = "+ res);
+
+    }
+
+
+}

SumOfProductsSubarray.java

@@ -0,0 +1,35 @@
+//package Backtracking-1;
+
+public class SumOfProductsSubarray {
+    long sum;
+    long prod;
+    boolean choose;
+    private long calSumOfProducts(int[] nums){
+        this.sum = 0;
+        this.prod = 1;
+        this.choose = true;
+        helper(nums, 0, prod, choose);
+        return sum;
+    }
+
+    private void helper(int[] nums, int idX, long prod, boolean choose){
+
+        //base
+        if(idX == nums.length) return;
+
+        //logic 
+        prod*=nums[idX];
+        System.out.println("prod = " + prod);
+        helper(nums, idX+1, sum + prod, true);
+        helper(nums, idX+1, prod, false);
+
+    }
+
+    public static void main(String[] args){
+        int[] nums = {2,3,6,7};
+        SumOfProductsSubarray solution  = new SumOfProductsSubarray();
+        long res = solution.calSumOfProducts(nums);
+        System.out.println("Sum of product of all sub arrays = " + res);
+    }
+
+}