LeetCode 389. Find the Difference

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Description

You are given two strings s and t.

String t is generated by random shuffling string s and then add one more letter at a random position.

Return the letter that was added to t.

Example 1:

Input: s = "abcd", t = "abcde"
Output: "e"
Explanation: 'e' is the letter that was added.
Example 2:

Input: s = "", t = "y"
Output: "y"

Constraints:

0 <= s.length <= 1000
t.length == s.length + 1
s and t consist of lowercase English letters.

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Analysis

Same as previous problem, we use an array to record the number of characters and compare with later string.

Solution written in Rust

impl Solution {
    pub fn find_the_difference(s: String, t: String) -> char {
        let mut alphas = [0; 26];
        s.chars().for_each(|c| {
            let i = c as usize - 'a' as usize;
            alphas[i] += 1;
        });

        for c in t.chars() {
            let i = c as usize - 'a' as usize;
            if alphas[i] == 0 {
                return c;
            }

            alphas[i] -= 1;
        }

        ' '
    }
}

Solution written in Cpp

class Solution {
public:
    char findTheDifference(string s, string t) {
        std::array<uint16_t, 26> chars {0};
        for (auto c: s) {
            chars[c - 'a']++;
        }

        for (auto c: t) {
            if (chars[c - 'a'] == 0) {
                return c;
            }
            chars[c - 'a']--;
        }

        return ' ';
    }
};

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https://review.gerrithub.io/c/robertwenhk/program-record/+/1193516