3223. Minimum Length of String After Operations 

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Description

You are given a string s.

You can perform the following process on s any number of times:

Choose an index i in the string such that there is at least one character to the left of index i that is equal to s[i], and at least one character to the right that is also equal to s[i].
Delete the closest occurrence of s[i] located to the left of i.
Delete the closest occurrence of s[i] located to the right of i.

Return the minimum length of the final string s that you can achieve.

Example 1:

Input: s = "abaacbcbb"

Output: 5

Explanation:
We do the following operations:

Choose index 2, then remove the characters at indices 0 and 3. The resulting string is s = "bacbcbb".
Choose index 3, then remove the characters at indices 0 and 5. The resulting string is s = "acbcb".

Example 2:

Input: s = "aa"

Output: 2

Explanation:
We cannot perform any operations, so we return the length of the original string.

Constraints:

1 <= s.length <= 2 * 10⁵
s consists only of lowercase English letters.

Solutions

Solution 1: Counting

We can count the occurrences of each character in the string, and then iterate through the count array. If a character appears an odd number of times, then $1$ of that character remains in the end; if a character appears an even number of times, then $2$ of that character remain. We can sum the remaining counts of all characters to get the final length of the string.

The time complexity is $O(n)$, where $n$ is the length of the string $s$. The space complexity is $O(|\Sigma|)$, where $|\Sigma|$ is the size of the character set, which is $26$ in this problem.

Python3

class Solution:
    def minimumLength(self, s: str) -> int:
        cnt = Counter(s)
        return sum(1 if x & 1 else 2 for x in cnt.values())

Java

class Solution {
    public int minimumLength(String s) {
        int[] cnt = new int[26];
        for (int i = 0; i < s.length(); ++i) {
            ++cnt[s.charAt(i) - 'a'];
        }
        int ans = 0;
        for (int x : cnt) {
            if (x > 0) {
                ans += x % 2 == 1 ? 1 : 2;
            }
        }
        return ans;
    }
}

C++

class Solution {
public:
    int minimumLength(string s) {
        int cnt[26]{};
        for (char& c : s) {
            ++cnt[c - 'a'];
        }
        int ans = 0;
        for (int x : cnt) {
            if (x) {
                ans += x % 2 ? 1 : 2;
            }
        }
        return ans;
    }
};

Go

func minimumLength(s string) (ans int) {
	cnt := [26]int{}
	for _, c := range s {
		cnt[c-'a']++
	}
	for _, x := range cnt {
		if x > 0 {
			if x&1 == 1 {
				ans += 1
			} else {
				ans += 2
			}
		}
	}
	return
}

TypeScript

function minimumLength(s: string): number {
    const cnt = new Map<string, number>();
    for (const c of s) {
        cnt.set(c, (cnt.get(c) || 0) + 1);
    }
    let ans = 0;
    for (const x of cnt.values()) {
        ans += x & 1 ? 1 : 2;
    }
    return ans;
}