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100 lines
2.7 KiB
Markdown
100 lines
2.7 KiB
Markdown
# [677. Map Sum Pairs](https://leetcode.com/problems/map-sum-pairs/)
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## 题目
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Design a map that allows you to do the following:
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- Maps a string key to a given value.
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- Returns the sum of the values that have a key with a prefix equal to a given string.
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Implement the `MapSum` class:
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- `MapSum()` Initializes the `MapSum` object.
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- `void insert(String key, int val)` Inserts the `key-val` pair into the map. If the `key` already existed, the original `key-value` pair will be overridden to the new one.
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- `int sum(string prefix)` Returns the sum of all the pairs' value whose `key` starts with the `prefix`.
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**Example 1:**
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```
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Input
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["MapSum", "insert", "sum", "insert", "sum"]
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[[], ["apple", 3], ["ap"], ["app", 2], ["ap"]]
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Output
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[null, null, 3, null, 5]
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Explanation
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MapSum mapSum = new MapSum();
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mapSum.insert("apple", 3);
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mapSum.sum("ap"); // return 3 (apple = 3)
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mapSum.insert("app", 2);
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mapSum.sum("ap"); // return 5 (apple +app = 3 + 2 = 5)
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```
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**Constraints:**
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- `1 <= key.length, prefix.length <= 50`
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- `key` and `prefix` consist of only lowercase English letters.
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- `1 <= val <= 1000`
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- At most `50` calls will be made to `insert` and `sum`.
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## 题目大意
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实现一个 MapSum 类，支持两个方法，insert 和 sum：
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- MapSum() 初始化 MapSum 对象
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- 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。
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- int sum(string prefix) 返回所有以该前缀 prefix 开头的键 key 的值的总和。
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## 解题思路
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- 简单题。用一个 map 存储数据，Insert() 方法即存储 key-value。Sum() 方法即累加满足条件前缀对应的 value。判断是否满足条件，先根据前缀长度来判断，只有长度大于等于 prefix 长度才可能满足要求。如果 key 是具有 prefix 前缀的，那么累加上这个值。最后输出总和即可。
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## 代码
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```go
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package leetcode
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type MapSum struct {
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keys map[string]int
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}
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/** Initialize your data structure here. */
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func Constructor() MapSum {
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return MapSum{make(map[string]int)}
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}
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func (this *MapSum) Insert(key string, val int) {
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this.keys[key] = val
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}
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func (this *MapSum) Sum(prefix string) int {
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prefixAsRunes, res := []rune(prefix), 0
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for key, val := range this.keys {
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if len(key) >= len(prefix) {
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shouldSum := true
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for i, char := range key {
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if i >= len(prefixAsRunes) {
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break
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}
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if prefixAsRunes[i] != char {
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shouldSum = false
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break
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}
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}
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if shouldSum {
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res += val
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}
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}
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}
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return res
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}
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/**
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* Your MapSum object will be instantiated and called as such:
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* obj := Constructor();
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* obj.Insert(key,val);
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* param_2 := obj.Sum(prefix);
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*/
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``` |