Merge pull request #2857 from realtmxi/master

[Fix][DP][Target Sum] python 2D version solution

Author: youngyangyang04

problems/0494.目标和.md

@@ -670,18 +670,26 @@ class Solution:
 
         # 创建二维动态规划数组，行表示选取的元素数量，列表示累加和
         dp = [[0] * (target_sum + 1) for _ in range(len(nums) + 1)]
+        dp = [[0] * (target_sum + 1) for _ in range(len(nums))]
 
         # 初始化状态
         dp[0][0] = 1
+        if nums[0] <= target_sum:
+            dp[0][nums[0]] = 1
+        numZero = 0
+        for i in range(len(nums)):
+            if nums[i] == 0:
+                numZero += 1
+            dp[i][0] = int(math.pow(2, numZero))
 
         # 动态规划过程
-        for i in range(1, len(nums) + 1):
+        for i in range(1, len(nums)):
             for j in range(target_sum + 1):
                 dp[i][j] = dp[i - 1][j]  # 不选取当前元素
                 if j >= nums[i - 1]:
-                    dp[i][j] += dp[i - 1][j - nums[i - 1]]  # 选取当前元素
+                    dp[i][j] += dp[i - 1][j - nums[i]]  # 选取当前元素
 
-        return dp[len(nums)][target_sum]  # 返回达到目标和的方案数
+        return dp[len(nums)-1][target_sum]  # 返回达到目标和的方案数
 
 
 ```