键值映射

题目

设计一个 map, 满足以下几点:

• 字符串表示键, 整数表示值.
• 返回具有前缀等于给定字符串的键的值的总和.

实现一个 MapSum 类:

• 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 key-value 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

MapSum mapSum = new MapSum();
mapSum.insert("apple", 3);
mapSum.sum("ap");           // 返回 3 (apple = 3)
mapSum.insert("app", 2);
mapSum.sum("ap");           // 返回 5 (apple + app = 3 + 2 = 5)

题解

比较简单, HashMap + String.prototype.startsWith 即可.

JavaScript

var MapSum = function () {
  this.map = new Map()
}

/**
 * @param {string} key
 * @param {number} val
 * @return {void}
 */
MapSum.prototype.insert = function (key, val) {
  this.map.set(key, val)
}

/**
 * @param {string} prefix
 * @return {number}
 */
MapSum.prototype.sum = function (prefix) {
  let sum = 0
  this.map.forEach((val, key) => {
    if (key.startsWith(prefix)) {
      sum += val
    }
  })

  return sum
}

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

Rust

use std::collections::HashMap;

struct MapSum {
    map: HashMap<String, i32>,
}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl MapSum {
    fn new() -> Self {
        MapSum {
            map: HashMap::new(),
        }
    }

    fn insert(&mut self, key: String, val: i32) {
        self.map.insert(key, val);
    }

    fn sum(&self, prefix: String) -> i32 {
        let mut sum = 0;
        for (key, val) in &self.map {
            if key.starts_with(&prefix) {
                sum += val;
            }
        }
        sum
    }
}

/**
 * Your MapSum object will be instantiated and called as such:
 * let obj = MapSum::new();
 * obj.insert(key, val);
 * let ret_2: i32 = obj.sum(prefix);
 */