Map Sum Pairs LeetCode Solution

Problem – Map Sum Pairs

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.

Map Sum Pairs LeetCode Solution in C++

class MapSum {
public:
    /** Initialize your data structure here. */    
    void insert(string key, int val) {
        mp[key] = val;
    }
    
    int sum(string prefix) {
        int sum = 0, n = prefix.size();
        for (auto it = mp.lower_bound(prefix); it != mp.end() && it->first.substr(0, n) == prefix; it++) 
            sum += it->second;
        return sum;
    }
private:
    map<string, int> mp;
};

Map Sum Pairs LeetCode Solution in Java

class MapSum {
    class TrieNode {
        Map<Character, TrieNode> children;
        boolean isWord;
        int value;

        public TrieNode() {
            children = new HashMap<Character, TrieNode>();
            isWord = false;
            value = 0;
        }
    }
    
    TrieNode root;
    
    /** Initialize your data structure here. */
    public MapSum() {
        root = new TrieNode();
    }
    
    public void insert(String key, int val) {
        TrieNode curr = root;
        for (char c : key.toCharArray()) {
            TrieNode next = curr.children.get(c);
            if (next == null) {
                next = new TrieNode();
                curr.children.put(c, next);
            }
            curr = next;
        }
        curr.isWord = true;
        curr.value = val;
    }
    
    public int sum(String prefix) {
        TrieNode curr = root;
	for (char c : prefix.toCharArray()) {
	    TrieNode next = curr.children.get(c);
	    if (next == null) {
	        return 0;
	    }
	    curr = next;
        }
		
        return dfs(curr);
    }
    
    private int dfs(TrieNode root) {
        int sum = 0;
        for (char c : root.children.keySet()) {
            sum += dfs(root.children.get(c));
        }
        return sum + root.value;
    }
}

Map Sum Pairs LeetCode Solution in Python

class MapSum(object):

    def __init__(self): 
        self.d = {}

    def insert(self, key, val): 
        self.d[key] = val

    def sum(self, prefix):
        return sum(self.d[i] for i in self.d if i.startswith(prefix))
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