Skip to content

1544. Make The String Great

Description

Given a string s of lower and upper case English letters.

A good string is a string which doesn't have two adjacent characters s[i] and s[i + 1] where:

  • 0 <= i <= s.length - 2
  • s[i] is a lower-case letter and s[i + 1] is the same letter but in upper-case or vice-versa.

To make the string good, you can choose two adjacent characters that make the string bad and remove them. You can keep doing this until the string becomes good.

Return the string after making it good. The answer is guaranteed to be unique under the given constraints.

Notice that an empty string is also good.

 

Example 1:

Input: s = "leEeetcode"
Output: "leetcode"
Explanation: In the first step, either you choose i = 1 or i = 2, both will result "leEeetcode" to be reduced to "leetcode".

Example 2:

Input: s = "abBAcC"
Output: ""
Explanation: We have many possible scenarios, and all lead to the same answer. For example:
"abBAcC" --> "aAcC" --> "cC" --> ""
"abBAcC" --> "abBA" --> "aA" --> ""

Example 3:

Input: s = "s"
Output: "s"

 

Constraints:

  • 1 <= s.length <= 100
  • s contains only lower and upper case English letters.

Solutions

Solution 1

Thinking

A “great” string has no adjacent letters that differ only in case. Repeated left-to-right deletions work for \(n\le 100\), but a deletion can create a new pair further left, forcing extra passes.

A stack holds the cleaned prefix. If the new character differs from the top by \(32\) (exactly a case pair), pop; otherwise push. One linear scan produces the answer.

1
2
3
4
5
6
7
8
9
class Solution:
    def makeGood(self, s: str) -> str:
        stk = []
        for c in s:
            if not stk or abs(ord(stk[-1]) - ord(c)) != 32:
                stk.append(c)
            else:
                stk.pop()
        return "".join(stk)

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
class Solution {
    public String makeGood(String s) {
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            if (sb.length() == 0 || Math.abs(sb.charAt(sb.length() - 1) - c) != 32) {
                sb.append(c);
            } else {
                sb.deleteCharAt(sb.length() - 1);
            }
        }
        return sb.toString();
    }
}

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
class Solution {
public:
    string makeGood(string s) {
        string stk;
        for (char c : s) {
            if (stk.empty() || abs(stk.back() - c) != 32) {
                stk += c;
            } else {
                stk.pop_back();
            }
        }
        return stk;
    }
};

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
func makeGood(s string) string {
    stk := []rune{}
    for _, c := range s {
        if len(stk) == 0 || abs(int(stk[len(stk)-1]-c)) != 32 {
            stk = append(stk, c)
        } else {
            stk = stk[:len(stk)-1]
        }
    }
    return string(stk)
}

func abs(x int) int {
    if x < 0 {
        return -x
    }
    return x
}

Comments