Target Sum: Accepted

Author: gouthampradhan

README.md

@@ -43,6 +43,7 @@ My accepted leetcode solutions to some of the common interview problems.
 - [Remove Invalid Parentheses](problems/src/backtracking/RemoveInvalidParentheses.java) (Medium)
 - [Regular Expression Matching](problems/src/backtracking/RegularExpressionMatching.java) (Hard)
 - [Expression Add Operators](problems/src/backtracking/ExpressionAddOperators.java) (Hard)
+- [Expression Add Operators](problems/src/backtracking/ExpressionAddOperators.java) (Hard)
 
 #### [Binary Search](problems/src/binary_search)
 
@@ -54,7 +55,7 @@ My accepted leetcode solutions to some of the common interview problems.
 - [Median of Two Sorted Arrays](problems/src/binary_search/MedianOfTwoSortedArrays.java) (Hard)
 - [Pow(x, n)](problems/src/binary_search/PowXN.java) (Medium)
 - [Find Peak Element](problems/src/binary_search/FindPeakElement.java) (Medium)
-- [First Bad Version](problems/src/binary_search/FirstBadVersion.java) (Easy)
+- [Target Sum](problems/src/binary_search/TargetSum.java) (Medium)
 
 #### [Bit Manipulation](problems/src/bit_manipulation)
 

problems/src/backtracking/TargetSum.java

@@ -0,0 +1,60 @@
+package backtracking;
+
+/**
+ * Created by gouthamvidyapradhan on 09/12/2017.
+ * You are given a list of non-negative integers, a1, a2, ..., an, and a target, S. Now you have 2 symbols + and -.
+ * For each integer, you should choose one from + and - as its new symbol.
+
+ Find out how many ways to assign symbols to make sum of integers equal to target S.
+
+ Example 1:
+ Input: nums is [1, 1, 1, 1, 1], S is 3.
+ Output: 5
+ Explanation:
+
+ -1+1+1+1+1 = 3
+ +1-1+1+1+1 = 3
+ +1+1-1+1+1 = 3
+ +1+1+1-1+1 = 3
+ +1+1+1+1-1 = 3
+
+ There are 5 ways to assign symbols to make the sum of nums be target 3.
+ Note:
+ The length of the given array is positive and will not exceed 20.
+ The sum of elements in the given array will not exceed 1000.
+ Your output answer is guaranteed to be fitted in a 32-bit integer.
+ *
+ */
+public class TargetSum {
+
+    private static int n;
+    /**
+     * Main method
+     * @param args
+     * @throws Exception
+     */
+    public static void main(String[] args) throws Exception{
+        int[] A = {1, 1, 1, 1, 1};
+        n = 0;
+        new TargetSum().findTargetSumWays(A, 3);
+        System.out.println(n);
+    }
+
+    public int findTargetSumWays(int[] nums, int S) {
+        backtrack(nums, S, 0, 0);
+        return n;
+    }
+
+    private void backtrack(int[] nums, int target, int sum, int i){
+        if(i == nums.length){
+            if(sum == target){
+                n++;
+            }
+        } else{
+            backtrack(nums, target, sum + nums[i], i + 1);
+            backtrack(nums, target, sum - nums[i], i + 1);
+        }
+    }
+
+}
+