Sword finger offer II 066. sum of words (medium prefix tree design string)

The finger of the sword Offer II 066. Sum of words

Achieve one MapSum class , Two methods are supported ,insert and sum：

MapSum() initialization MapSum object
void insert(String key, int val) Insert key-val Key value pair , Strings represent keys key , Integers represent values val . If key key Already exist , Then the original key value pair will be replaced by the new key value pair .
int sum(string prefix) Returns all with this prefix prefix Key at the beginning key The sum of the values of .

Example ：

Input ：
inputs = [“MapSum”, “insert”, “sum”, “insert”, “sum”]
inputs = [[], [“apple”, 3], [“ap”], [“app”, 2], [“ap”]]
Output ：
[null, null, 3, null, 5]

explain ：
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)

Tips ：

1 <= key.length, prefix.length <= 50
key and prefix It's only made up of lowercase letters
1 <= val <= 1000
Call at most 50 Time insert and sum

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/z1R5dt
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

analysis

When constructing nodes of prefix tree , Assign values to nodes , In the insert key When , Assign a value at the end node val, stay sum In the method , The shilling node points to the end of the prefix string , And then use it dfs（ Here is getSum Method ）, Get the values of all the leaf nodes of the subtree .

Answer key （Java）

class MapSum {
    
    static class TrieNode {
    
        public TrieNode[] children;
        public int val;

        public TrieNode() {
    
            children = new TrieNode[26];
        }
    }

    private TrieNode root;

    /** Initialize your data structure here. */
    public MapSum() {
    
        root = new TrieNode();
    }
    
    public void insert(String key, int val) {
    
        boolean f = false;
        TrieNode node = root;
        for (char ch : key.toCharArray()) {
    
            if (node.children[ch - 'a'] == null) {
    
                f = true;
                node.children[ch - 'a'] = new TrieNode();
            }
            node = node.children[ch - 'a'];
        }
        node.val = val;
    }
    
    public int sum(String prefix) {
    
        TrieNode node = root;
        for (char ch : prefix.toCharArray()) {
    
            if (node.children[ch - 'a'] == null) {
    
                return 0;
            }

            node = node.children[ch - 'a'];
        }
        return getSum(node);
    }

    private int getSum(TrieNode node) {
    
        if (node == null) {
    
            return 0;
        }

        int ans = node.val;
        for (TrieNode child : node.children) {
    
            ans += getSum(child);
        }

        return ans;
    }
}

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