677. Map Sum Pairs

Medium (Trung bình) Python 🔗 Xem trên LeetCode

📋 Đề Bài

Design a map that allows you to do the following:

  • Maps a string key to a given value.
  • Returns the sum of the values that have a key with a prefix equal to a given string.

Implement the MapSum class:

  • MapSum() Initializes the MapSum object.
  • void insert(String key, int val) Inserts the key-val pair into the map. If the key already existed, the original key-value pair will be overridden to the new one.
  • int sum(string prefix) Returns the sum of all the pairs' value whose key starts with the prefix.

 

Example 1:

Input
["MapSum", "insert", "sum", "insert", "sum"]
[[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
Output
[null, null, 3, null, 5]

Explanation
MapSum mapSum = new MapSum();
mapSum.insert("apple", 3);  
mapSum.sum("ap");           // return 3 (apple = 3)
mapSum.insert("app", 2);    
mapSum.sum("ap");           // return 5 (apple + app = 3 + 2 = 5)

 

Constraints:

  • 1 <= key.length, prefix.length <= 50
  • key and prefix consist of only lowercase English letters.
  • 1 <= val <= 1000
  • At most 50 calls will be made to insert and sum.

🧠 Thuật Toán & Kỹ Thuật

Hash Table (Bảng băm)Union Find (Tập hợp rời rạc)Trie (Cây tiền tố)Prefix Sum (Tổng tiền tố)
⏱️ Thời gian O(n²)
💾 Không gian O(n)

💻 Lời Giải

Python 0677-map-sum-pairs.py 
class Node:
    def __init__(self):
        self.total = 0
        self.children = defaultdict(Node)
        
class Trie:
    def __init__(self):
        self.root = Node()
    
    def insert(self, word: str, diff: int) -> None:
        root = self.root
        for char in word:
            root = root.children[char]
            root.total += diff
        
    def find(self, prefix: str) -> int:
        root = self.root
        for char in prefix:
            if char not in root.children:
                return 0
            root = root.children[char]
        
        return root.total
    
class MapSum:

    def __init__(self):
        self.trie = Trie()
        self.umap = defaultdict(int)

    def insert(self, key: str, val: int) -> None:
        diff = val - self.umap[key]
        self.trie.insert(key, diff)
        self.umap[key] = val

    def sum(self, prefix: str) -> int:
        return self.trie.find(prefix)


# Your MapSum object will be instantiated and called as such:
# obj = MapSum()
# obj.insert(key,val)
# param_2 = obj.sum(prefix)