Update dp.md

update backpack

Author: eadst

basic_algorithm/dp.md

@@ -736,7 +736,32 @@ class Solution:
 ```
 
 ```Python
+def backPack(weight, value, bagweight):
+    # 二维数组
+    dp = [[0] * (bagweight + 1) for _ in range(len(weight))]
+
+    # 初始化
+    for j in range(weight[0], bagweight + 1):
+        dp[0][j] = value[0]
+
+    # weight数组的大小就是物品个数
+    for i in range(1, len(weight)):  # 遍历物品
+        for j in range(bagweight + 1):  # 遍历背包容量
+            if j < weight[i]:
+                dp[i][j] = dp[i - 1][j]
+            else:
+                dp[i][j] = max(dp[i - 1][j], dp[i - 1][j - weight[i]] + value[i])
+
+    return dp[len(weight) - 1][bagweight]
+
+if __name__ == "__main__":
+
+    weight = [1, 3, 4]
+    value = [15, 20, 30]
+    bagweight = 4
 
+    result = backPack(weight, value, bagweight)
+    print(result)
 ```
 
 ### [backpack-ii](https://www.lintcode.com/problem/backpack-ii/description)