MapSum.java

package trie;

import java.util.TreeMap;

class MapSum {

    public class Node {
        public int value;
        public TreeMap<Character, Node> next;

        public Node(int value) {
            this.value = value;
            next = new TreeMap<>();
        }

        public Node() {
            this(0);
        }
    }

    Node root;

    /** Initialize your data structure here. */
    public MapSum() {
        root = new Node();
    }

    public void insert(String key, int val) {

        Node cur = root;
        for (int i = 0; i < key.length(); i++) {
            char c = key.charAt(i);
            if (cur.next.get(c) == null) {
                cur.next.put(c, new Node());
            }
            cur = cur.next.get(c);
        }

        cur.value = val;
    }

    public int sum(String prefix) {

        Node cur = root;
        for (int i = 0; i < prefix.length(); i++) {
            char c = prefix.charAt(i);
            if (cur.next.get(c) == null) {
                return 0;
            }
            cur = cur.next.get(c);
        }

        return sum(cur);
    }

    private int sum(Node cur) {

        int res = cur.value;
        for(char c:cur.next.keySet()) {
            res += sum(cur.next.get(c));
        }
        return res;
    }

}

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