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389. Find the Difference 👍

Approach 1: Bit

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  char findTheDifference(string s, string t) {
    char ans = 0;

    for (const char c : s)
      ans ^= c;

    for (const char c : t)
      ans ^= c;

    return ans;
  }
};

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class Solution {
  public char findTheDifference(String s, String t) {
    char ans = 0;

    for (final char c : s.toCharArray())
      ans ^= c;

    for (final char c : t.toCharArray())
      ans ^= c;

    return ans;
  }
}

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class Solution:
  def findTheDifference(self, s: str, t: str) -> str:
    count = collections.Counter(s)

    for i, c in enumerate(t):
      count[c] -= 1
      if count[c] == -1:
        return c

Approach 2: Hash Table

  • Time: $O(n)$
  • Space: $O(1)$
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class Solution {
 public:
  char findTheDifference(string s, string t) {
    vector<int> count(128);

    for (const char c : s)
      ++count[c];

    for (const char c : t)
      if (--count[c] < 0)
        return c;

    throw;
  }
};

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class Solution {
  public char findTheDifference(String s, String t) {
    int[] count = new int[128];

    for (final char c : s.toCharArray())
      ++count[c];

    for (final char c : t.toCharArray())
      if (--count[c] < 0)
        return c;

    throw new IllegalArgumentException();
  }
}