英文:
Fetching all keys for unique value in treemap in JAVA
问题
我有一个树图，其中以国家为值，相应的州/省为键，使得键是唯一的，而值是重复的。我想通过传递特定的国家来获取所有键（即我想获取该国家的所有州/省）。我该如何做到这一点？如果需要提供其他任何信息，请告诉我。
英文:
I have a treemap which has countries as values and corresponding states as keys such that keys are unique and values are duplicate. I want to fetch all keys for a unique value (i.e. I want to fetch all the states of a country by passing that particular country). How do I do that? Let me know if I need to provide any other information.
答案1
得分: 0
这里是一些代码，希望能帮助你开始。从你的帖子中可以观察到，在 Map 中，给定的键不能有多个值。值需要是一个列表或另一个可以容纳多个值的对象类型。
String search = "Mexico";// 创建 TreeMapMap<String, String> stateMap = new TreeMap();stateMap.put("CO", "USA");stateMap.put("Ontario", "Canada");stateMap.put("Chiapas", "Mexico");stateMap.put("Chihuahua", "Mexico");stateMap.put("TX", "USA");stateMap.put("GA", "USA");// HashSet 将存储在搜索国家中找到的唯一状态列表Set<String> results = new HashSet();// 遍历源 TreeMap，寻找与搜索字符串匹配的国家for (String state : stateMap.keySet()) {String country = stateMap.get(state);if (country.equals(search)) {results.add(state);}}// 遍历结果集并打印搜索国家的每个状态results.forEach(state -> System.out.println(state));
英文:
Here is some code that will hopefully get you going. One observation from your post is that you cannot have more than one value for a given key in a Map. The value would need to be a list or another object type that can hold multiple values.
String search = "Mexico";// create our TreeMapMap<String, String> stateMap = new TreeMap();stateMap.put("CO", "USA");stateMap.put("Ontario", "Canada");stateMap.put("Chiapas", "Mexico");stateMap.put("Chihuahua", "Mexico");stateMap.put("TX", "USA");stateMap.put("GA", "USA");// HashSet will store the unique list of states found in the search countrySet<String> results = new HashSet();// iterate over the source TreeMap looking for the country to match the search stringfor (String state : stateMap.keySet()) {String country = stateMap.get(state);if (country.equals(search)) {results.add(state);}}// iterate through the results set and print each state for the search countryresults.forEach(state -> System.out.println(state));</details>
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