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added: target sum

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	`1`	`+# target sum \| leetcode 494 \| https://leetcode.com/problems/target-sum/`
	`2`	`+# 0/1 knapsack to decide +/- and cache (index, total)`
	`3`	`+`
	`4`	`+class Solution:`
	`5`	`+ def findTargetSumWays(self, nums: list[int], target: int) -> int:`
	`6`	`+ N = len(nums)`
	`7`	`+ mem = dict()`
	`8`	`+`
	`9`	`+ if N == 0:`
	`10`	`+ return 0`
	`11`	`+`
	`12`	`+ def knapsack(n, s):`
	`13`	`+ if n == N:`
	`14`	`+ return 1 if s == target else 0`
	`15`	`+`
	`16`	`+ if (n, s) in mem:`
	`17`	`+ return mem[(n, s)]`
	`18`	`+`
	`19`	`+ mem[(n, s)] = knapsack(n+1, s + nums[n]) + knapsack(n+1, s - nums[n])`
	`20`	`+ return mem[(n, s)]`
	`21`	`+`
	`22`	`+ return knapsack(0, 0)`

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