Question

剑指 Offer II 066. 单词之和

题目描述

实现一个 MapSum 类，支持两个方法，insert 和 sum：

• MapSum() 初始化 MapSum 对象
• void insert(String key, int val) 插入 key-val 键值对，字符串表示键 key ，整数表示值 val 。如果键 key 已经存在，那么原来的键值对将被替代成新的键值对。
• int sum(string prefix) 返回所有以该前缀 prefix 开头的键 key 的值的总和。

 

示例：

输入：
inputs = ["MapSum", "insert", "sum", "insert", "sum"]
inputs = [[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
输出：
[null, null, 3, null, 5]

解释：
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)

 

提示：

• 1 <= key.length, prefix.length <= 50
• key 和 prefix 仅由小写英文字母组成
• 1 <= val <= 1000
• 最多调用 50 次 insert 和 sum

 

注意：本题与主站 677 题相同： https://leetcode.cn/problems/map-sum-pairs/

解法

方法一

class MapSum:
  def __init__(self):
    """
    Initialize your data structure here.
    """
    self.data = defaultdict(int)
    self.t = defaultdict(int)

  def insert(self, key: str, val: int) -> None:
    old = self.t[key]
    self.t[key] = val
    for i in range(1, len(key) + 1):
      self.data[key[:i]] += val - old

  def sum(self, prefix: str) -> int:
    return self.data[prefix]


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

class MapSum {
  private Map<String, Integer> data;
  private Map<String, Integer> t;

  /** Initialize your data structure here. */
  public MapSum() {
    data = new HashMap<>();
    t = new HashMap<>();
  }

  public void insert(String key, int val) {
    int old = t.getOrDefault(key, 0);
    t.put(key, val);
    for (int i = 1; i < key.length() + 1; ++i) {
      String k = key.substring(0, i);
      data.put(k, data.getOrDefault(k, 0) + (val - old));
    }
  }

  public int sum(String prefix) {
    return data.getOrDefault(prefix, 0);
  }
}

/**
 * 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 MapSum {
public:
  unordered_map<string, int> data;
  unordered_map<string, int> t;

  /** Initialize your data structure here. */
  MapSum() {
  }

  void insert(string key, int val) {
    int old = t[key];
    t[key] = val;
    for (int i = 1; i < key.size() + 1; ++i) {
      string k = key.substr(0, i);
      data[k] += (val - old);
    }
  }

  int sum(string prefix) {
    return data[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);
 */

type MapSum struct {
  data map[string]int
  t  map[string]int
}

/** Initialize your data structure here. */
func Constructor() MapSum {
  return MapSum{
    data: make(map[string]int),
    t:  make(map[string]int),
  }
}

func (this *MapSum) Insert(key string, val int) {
  old := this.t[key]
  this.t[key] = val
  for i := 1; i < len(key)+1; i++ {
    k := key[:i]
    this.data[k] += (val - old)
  }
}

func (this *MapSum) Sum(prefix string) int {
  return this.data[prefix]
}

/**
 * Your MapSum object will be instantiated and called as such:
 * obj := Constructor();
 * obj.Insert(key,val);
 * param_2 := obj.Sum(prefix);
 */