feat: add swift solution 2 implementation to lcof2 problem: No.102 (doocs#3615)

Author: klever34

lcof2/剑指 Offer II 102. 加减的目标值/README.md

@@ -241,6 +241,29 @@ func findTargetSumWays(nums []int, target int) int {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func findTargetSumWays(_ nums: [Int], _ target: Int) -> Int {
+        let s = nums.reduce(0, +)
+        if s - target < 0 || (s - target) % 2 != 0 {
+            return 0
+        }
+        let target = (s - target) / 2
+        var dp = [Int](repeating: 0, count: target + 1)
+        dp[0] = 1
+
+        for num in nums {
+            for j in stride(from: target, through: num, by: -1) {
+                dp[j] += dp[j - num]
+            }
+        }
+        return dp[target]
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 102. 加减的目标值/Solution2.swift

@@ -0,0 +1,18 @@
+class Solution {
+    func findTargetSumWays(_ nums: [Int], _ target: Int) -> Int {
+        let s = nums.reduce(0, +)
+        if s - target < 0 || (s - target) % 2 != 0 {
+            return 0
+        }
+        let target = (s - target) / 2
+        var dp = [Int](repeating: 0, count: target + 1)
+        dp[0] = 1
+        
+        for num in nums {
+            for j in stride(from: target, through: num, by: -1) {
+                dp[j] += dp[j - num]
+            }
+        }
+        return dp[target]
+    }
+}