LeetCode 243. Shortest Word Distance

最新推荐文章于 2023-12-19 11:46:25 发布

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最新推荐文章于 2023-12-19 11:46:25 发布

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本文提供了一种高效的C++算法来计算列表中两个指定单词之间的最短距离，通过两种方法实现：一种是记录单词索引并计算距离，另一种使用哈希表以O(N)时间复杂度解决。

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Two methods. Hashmap is not quite useful here.

#include <string>
#include <vector>
#include <iostream>
#include <climits>
#include <unordered_map>
using namespace std;

/*
  Given a list of words and two words word1 and word2, return the shorest distance between these
  two words in the list.
  for example:
  words = ["practise", "make", "perfect", "coding", "makes"]
  word1 = "coding", word2 = "practice", return 3.
  word1 = "makes", word2 = "coding", return 1.
  Note: you may assume that word1 does not equal to word2, and word1 and word2 are both in the list.
*/
// method1, remember two words' index and caculate the distance. O(N) time. O(1) space.
int shortestDistance(vector<string>& words, string word1, string word2) {
  int index_1 = -1;
  int index_2 = -1;
  int minDistance = INT_MAX;
  for(int i = 0; i < words.size(); ++i) {
    if(words[i] == word1) index_1 = i;
    if(words[i] == word2) index_2 = i;
    if(index_1 != -1 && index_2 != -1) {
      minDistance = min(minDistance, abs(index_1 - index_2));
    }
  }
  return minDistance;
}

// method2: we can use hashmap. O(N) time, O(N) space.
int shortestDistanceII(vector<string>& words, string word1, string word2) {
  unordered_map<string, int> wordsToIndex;
  int minDistance = INT_MAX;
  for(int i = 0; i < words.size(); ++i) {
    auto iter_word1 = wordsToIndex.find(word1);
    auto iter_word2 = wordsToIndex.find(word2);
    // unordered_map only support unique key insert. duplicates using unordered_multimap.
    if(iter_word1 == wordsToIndex.end()) wordsToIndex.insert({words[i], i});
    else wordsToIndex[words[i]] = i;
    if(iter_word2 == wordsToIndex.end()) wordsToIndex.insert({words[i], i});
    else wordsToIndex[words[i]] = i;
    if((iter_word1 != wordsToIndex.end()) && (iter_word2 != wordsToIndex.end())) {
      minDistance = min(minDistance, abs(iter_word1->second - iter_word2->second));
    }
  }
  return minDistance;
}

int main(void) {
  vector<string> words{"practise", "make", "perfect", "coding", "make"};
  int dis = shortestDistanceII(words, "make", "coding");
  cout << dis << endl;
}