Target Sum

Similar Problems:

- Series: TwoSum Problems & Follow-Up
- Expression Add Operators
- CheatSheet: Leetcode For Code Interview
- Tag: #bfs, #twosum

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

// Blog link: https://code.dennyzhang.com/target-sum // Basic Ideas: BFS + hashmap // Complexity: Time O(pow(2, n)), Space O(1) // The value would be in between -1000 and 1000 // Thus Space is O(1) func findTargetSumWays(nums []int, S int) int { m := make(map[int]int) m[0] = 1 for _, num := range nums { m2 := make(map[int]int) for v := range m { m2[v+num] += m[v] m2[v-num] += m[v] } m = m2 } return m[S] }