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map-sum-pairs.py
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map-sum-pairs.py
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# Time: O(n), n is the length of key
# Space: O(t), t is the number of nodes in trie
# Implement a MapSum class with insert, and sum methods.
#
# For the method insert, you'll be given a pair of (string, integer).
# The string represents the key and the integer represents the value.
# If the key already existed, then the original key-value pair will be overridden to the new one.
#
# For the method sum, you'll be given a string representing the prefix,
# and you need to return the sum of all the pairs' value whose key starts with the prefix.
#
# Example 1:
# Input: insert("apple", 3), Output: Null
# Input: sum("ap"), Output: 3
# Input: insert("app", 2), Output: Null
# Input: sum("ap"), Output: 5
import collections
class MapSum(object):
def __init__(self):
"""
Initialize your data structure here.
"""
_trie = lambda: collections.defaultdict(_trie)
self.__root = _trie()
def insert(self, key, val):
"""
:type key: str
:type val: int
:rtype: void
"""
# Time: O(n)
curr = self.__root
for c in key:
curr = curr[c]
delta = val
if "_end" in curr:
delta -= curr["_end"]
curr = self.__root
for c in key:
curr = curr[c]
if "_count" in curr:
curr["_count"] += delta
else:
curr["_count"] = delta
curr["_end"] = val
def sum(self, prefix):
"""
:type prefix: str
:rtype: int
"""
# Time: O(n)
curr = self.__root
for c in prefix:
if c not in curr:
return 0
curr = curr[c]
return curr["_count"]
# Your MapSum object will be instantiated and called as such:
# obj = MapSum()
# obj.insert(key,val)
# param_2 = obj.sum(prefix)