[Swift]LeetCode677. 键值映射 | Map Sum Pairs

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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

---

实现一个 MapSum 类里的两个方法，insert 和 sum。

对于方法 insert，你将得到一对（字符串，整数）的键值对。字符串表示键，整数表示值。如果键已经存在，那么原来的键值对将被替代成新的键值对。

对于方法 sum，你将得到一个表示前缀的字符串，你需要返回所有以该前缀开头的键的值的总和。

示例 1:

输入: insert("apple", 3), 输出: Null
输入: sum("ap"), 输出: 3
输入: insert("app", 2), 输出: Null
输入: sum("ap"), 输出: 5

---

Runtime: 12 ms

Memory Usage: 19.9 MB

class MapSum {
    var m:[String:[Int]] 

    /** Initialize your data structure here. */
    init() {
        m = [String:[Int]]()
    }
    
    func insert(_ key: String, _ val: Int) {
        var diff:Int = val - m[key,default:[0,0]][0]
        var n:Int = key.count
        m[key,default:[0,0]][0] = val
        for i in stride(from:n - 1,to:0,by:-1)
        {
            m[key.subString(0, i),default:[0,0]][1] += diff
        }
    }
    
    func sum(_ prefix: String) -> Int {
        return m[prefix,default:[0,0]][0] + m[prefix,default:[0,0]][1]      
    }
}

extension String {
    // 截取字符串：指定索引和字符数
    // - begin: 开始截取处索引
    // - count: 截取的字符数量
    func subString(_ begin:Int,_ count:Int) -> String {
        let start = self.index(self.startIndex, offsetBy: max(0, begin))
        let end = self.index(self.startIndex, offsetBy:  min(self.count, begin + count))
        return String(self[start..<end]) 
    }  
}

/**
 * Your MapSum object will be instantiated and called as such:
 * let obj = MapSum()
 * obj.insert(key, val)
 * let ret_2: Int = obj.sum(prefix)
 */ 

---

16ms

class MapSum {    
    private let root = TrieNode()

    /** Initialize your data structure here. */
    init() {
        
    }
    
    func insert(_ key: String, _ val: Int) {
        var node = root
        for c in key {
            let next = node.insert(c, val)
            node = next
        }
        node.sum = val
    }
    
    func sum(_ prefix: String) -> Int {
        var node = root
        for c in prefix {
            guard let next = node.search(c) else {
                return 0
            }
            node = next
        }
        return node.allSum()
    }
}

class TrieNode {
    
    var sum = 0
    private var map = [Character: TrieNode]()
    
    func insert(_ c: Character, _ val: Int) -> TrieNode {
        if let node = map[c] {
            return node
        }
        let node = TrieNode()
        map[c] = node
        return node
    }
    
    func search(_ c: Character) -> TrieNode? {
        return map[c]
    }
    
    func allSum() -> Int {
        var val = sum
        map.forEach {
            val += $1.allSum()
        }
        return val
    }    
}

---

28ms

class Node {
    var value: Character?
    var parent: Node?
    var children: [Character : Node] = [:]
    var sum: Int?
    
    init(value: Character? = nil, parent: Node? = nil) {
        self.value = value
        self.parent = parent
    }
    
    func add(letter: Character) {
        guard children[letter] == nil else { return }
        children[letter] = Node(value: letter, parent: self)
    }
}

class MapSum {
    let root = Node()
    
    init() {
        
    }
    
    func insert(_ key: String, _ val: Int) {
        guard !key.isEmpty else { return }
        var currentNode = root
        
        for char in key {
            currentNode.add(letter: char)
            guard let node = currentNode.children[char] else { continue }
            currentNode = node
        }
        
        currentNode.sum = val
    }
    
    func sum(_ prefix: String) -> Int {
        guard !prefix.isEmpty else { return 0 }
        var currentNode = root
        
        for char in prefix {
            if let node = currentNode.children[char] {
                currentNode = node
            } else {
                return 0
            }
        }
        
        return findWords(node: currentNode)
    }
    
    func findWords(node: Node) -> Int {
        var result = 0
        
        for child in node.children {
            result +=  findWords(node: child.value)
        }
        
        return result + (node.sum ?? 0)
    }
}