Today I have done leetcode's June LeetCoding Challenge with cpp.

June LeetCoding Challenge 18

Description

Prefix and Suffix Search

Design a special dictionary with some words that searchs the words in it by a prefix and a suffix.

Implement the WordFilter class:

• WordFilter(string[] words) Initializes the object with the words in the dictionary.
• f(string prefix, string suffix) Returns the index of the word in the dictionary, which has the prefix prefix and the suffix suffix. If there is more than one valid index, return the largest of them. If there is no such word in the dictionary, return -1.

Example 1:

Input
["WordFilter", "f"]
[[["apple"]], ["a", "e"]]
Output
[null, 0]

Explanation
WordFilter wordFilter = new WordFilter(["apple"]);
wordFilter.f("a", "e"); // return 0, because the word at index 0 has prefix = "a" and suffix = 'e".

Constraints:

• 1 <= words.length <= 15000
• 1 <= words[i].length <= 10
• 1 <= prefix.length, suffix.length <= 10
• words[i], prefix and suffix consist of lower-case English letters only.
• At most 15000 calls will be made to the function f.

Solution

class WordFilter {
  map<string, string> idx;
  unordered_map<string, int> ans;
public:
    WordFilter(vector<string>& words) {
      int cnt = 0;
      for(auto &word : words) {
        ans[word] = cnt++;
        int len = word.length();
        for(int i = 1; i <= len; ++i) {
          idx[word.substr(len - i) + "?" + word] = word;
        }
      }
    }
    
    int f(string prefix, string suffix) {
      auto target = suffix + "?" + prefix;
      auto it = idx.lower_bound(target);
      int answer = -1;
      while(it != idx.end() && it->first.rfind(target, 0) == 0) {
        answer = max(answer, ans[it->second]);
        ++it;
      }
      return answer;
    }
};

// Accepted
// 13/13 cases passed (713 ms)
// Your runtime beats 52.99 % of cpp submissions
// Your memory usage beats 90.67 % of cpp submissions (108.8 MB)