677. Map Sum Pairs

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.

Solutions

Solution 1

Python3JavaC++GoTypeScript

class Trie:
    def __init__(self):
        self.children: List[Trie | None] = [None] * 26
        self.val: int = 0

    def insert(self, w: str, x: int):
        node = self
        for c in w:
            idx = ord(c) - ord('a')
            if node.children[idx] is None:
                node.children[idx] = Trie()
            node = node.children[idx]
            node.val += x

    def search(self, w: str) -> int:
        node = self
        for c in w:
            idx = ord(c) - ord('a')
            if node.children[idx] is None:
                return 0
            node = node.children[idx]
        return node.val


class MapSum:
    def __init__(self):
        self.d = defaultdict(int)
        self.tree = Trie()

    def insert(self, key: str, val: int) -> None:
        x = val - self.d[key]
        self.d[key] = val
        self.tree.insert(key, x)

    def sum(self, prefix: str) -> int:
        return self.tree.search(prefix)


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

class Trie {
    private Trie[] children = new Trie[26];
    private int val;

    public void insert(String w, int x) {
        Trie node = this;
        for (int i = 0; i < w.length(); ++i) {
            int idx = w.charAt(i) - 'a';
            if (node.children[idx] == null) {
                node.children[idx] = new Trie();
            }
            node = node.children[idx];
            node.val += x;
        }
    }

    public int search(String w) {
        Trie node = this;
        for (int i = 0; i < w.length(); ++i) {
            int idx = w.charAt(i) - 'a';
            if (node.children[idx] == null) {
                return 0;
            }
            node = node.children[idx];
        }
        return node.val;
    }
}

class MapSum {
    private Map<String, Integer> d = new HashMap<>();
    private Trie trie = new Trie();

    public MapSum() {
    }

    public void insert(String key, int val) {
        int x = val - d.getOrDefault(key, 0);
        d.put(key, val);
        trie.insert(key, x);
    }

    public int sum(String prefix) {
        return trie.search(prefix);
    }
}

/**
 * Your MapSum object will be instantiated and called as such:
 * MapSum obj = new MapSum();
 * obj.insert(key,val);
 * int param_2 = obj.sum(prefix);
 */

class Trie {
public:
    Trie()
        : children(26, nullptr) {
    }

    void insert(string& w, int