2268. Minimum Number of Keypresses

Description

You have a keypad with 9 buttons, numbered from 1 to 9, each mapped to lowercase English letters. You can choose which characters each button is matched to as long as:

  • All 26 lowercase English letters are mapped to.
  • Each character is mapped to by exactly 1 button.
  • Each button maps to at most 3 characters.

To type the first character matched to a button, you press the button once. To type the second character, you press the button twice, and so on.

Given a string s, return the minimum number of keypresses needed to type s using your keypad.

Note that the characters mapped to by each button, and the order they are mapped in cannot be changed.

 

Example 1:

Input: s = "apple"
Output: 5
Explanation: One optimal way to setup your keypad is shown above.
Type 'a' by pressing button 1 once.
Type 'p' by pressing button 6 once.
Type 'p' by pressing button 6 once.
Type 'l' by pressing button 5 once.
Type 'e' by pressing button 3 once.
A total of 5 button presses are needed, so return 5.

Example 2:

Input: s = "abcdefghijkl"
Output: 15
Explanation: One optimal way to setup your keypad is shown above.
The letters 'a' to 'i' can each be typed by pressing a button once.
Type 'j' by pressing button 1 twice.
Type 'k' by pressing button 2 twice.
Type 'l' by pressing button 3 twice.
A total of 15 button presses are needed, so return 15.

 

Constraints:

  • 1 <= s.length <= 105
  • s consists of lowercase English letters.

Solutions

Solution 1

Python Code
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class Solution:
    def minimumKeypresses(self, s: str) -> int:
        cnt = Counter(s)
        ans = 0
        i, j = 0, 1
        for v in sorted(cnt.values(), reverse=True):
            i += 1
            ans += j * v
            if i % 9 == 0:
                j += 1
        return ans

Java Code
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class Solution {
    public int minimumKeypresses(String s) {
        int[] cnt = new int[26];
        for (char c : s.toCharArray()) {
            ++cnt[c - 'a'];
        }
        Arrays.sort(cnt);
        int ans = 0;
        for (int i = 1, j = 1; i <= 26; ++i) {
            ans += j * cnt[26 - i];
            if (i % 9 == 0) {
                ++j;
            }
        }
        return ans;
    }
}

C++ Code
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class Solution {
public:
    int minimumKeypresses(string s) {
        vector<int> cnt(26);
        for (char& c : s) ++cnt[c - 'a'];
        sort(cnt.begin(), cnt.end());
        int ans = 0;
        for (int i = 1, j = 1; i <= 26; ++i) {
            ans += j * cnt[26 - i];
            if (i % 9 == 0) ++j;
        }
        return ans;
    }
};

Go Code
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func minimumKeypresses(s string) int {
	cnt := make([]int, 26)
	for _, c := range s {
		cnt[c-'a']++
	}
	sort.Ints(cnt)
	ans := 0
	for i, j := 1, 1; i <= 26; i++ {
		ans += j * cnt[26-i]
		if i%9 == 0 {
			j++
		}
	}
	return ans
}