算法:同构字符串205. Isomorphic Strings

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题目

205. Isomorphic Strings

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

Example 1:

Input: s = "egg", t = "add"
Output: true

Example 2:

Input: s = "foo", t = "bar"
Output: false

Example 3:

Input: s = "paper", t = "title"
Output: true

Note:
You may assume both s and t have the same length.

解法

用双map记录单词出现的位置,如果出现过并且位置相同,则继续;否则就失败。
这里需要特别注意,遍历的时候要用Integer,因为即使相同的int装箱后也是不同的Integer对象。

package hashtable;

// https://leetcode.com/problems/isomorphic-strings/

import java.util.HashMap;
import java.util.Map;

public class IsomorphicStrings {
   
  public boolean isIsomorphic(String s, String t) {
   
    // check edge
    if (s == null || t == null) {
   
      return s == t;
    }
    int len = s.length();
    if (len != t.length()) {
   
      return false;
    }

    Map<Character, Integer> smap = new HashMap<>();
    Map<Character, Integer> tmap = new HashMap<>();
    for (Integer i = 0; i < len; i++) {
   
      char sc = s.charAt(i);
      char tc = t.charAt(i);
      addItem(smap, i, sc);
      addItem(tmap, i, tc);

      if (smap.get(sc) != tmap.get(tc)) {
   
        return false;
      }
    }

    return true;
  }

  private void addItem(Map<Character, Integer> map, Integer i, char c) {
   
    if (!map.containsKey(c)) {
   
      map.put(c, i);
    }
  }
}