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677. Map Sum Pairs

Difficulty Topics

Description

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.

Solution

map-sum-pairs.py
class TrieNode:
    def __init__(self):
        self.children = collections.defaultdict(TrieNode)
        self.value = 0

class Trie:
    def __init__(self):
        self.root = TrieNode()

    def insert(self, key, val):
        curr = self.root

        for c in key:
            curr = curr.children[c]

        curr.value = val

    def sumVal(self, prefix):
        curr = self.root

        for c in prefix:
            curr = curr.children[c]

        return self.dfs(curr)

    def dfs(self, curr):
        total = curr.value

        for char in curr.children:
            if curr.children[char]:
                total += self.dfs(curr.children[char])

        return total

class MapSum:

    def __init__(self):
        self.trie = Trie()

    def insert(self, key: str, val: int) -> None:
        self.trie.insert(key, val)

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


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