LeetCode-in-Java

3081. Replace Question Marks in String to Minimize Its Value

Medium

You are given a string s. s[i] is either a lowercase English letter or '?'.

For a string t having length m containing only lowercase English letters, we define the function cost(i) for an index i as the number of characters equal to t[i] that appeared before it, i.e. in the range [0, i - 1].

The value of t is the sum of cost(i) for all indices i.

For example, for the string t = "aab":

• cost(0) = 0
• cost(1) = 1
• cost(2) = 0
• Hence, the value of "aab" is 0 + 1 + 0 = 1.

Your task is to replace all occurrences of '?' in s with any lowercase English letter so that the value of s is minimized.

Return a string denoting the modified string with replaced occurrences of '?'. If there are multiple strings resulting in the minimum value, return the lexicographically smallest one.

Example 1:

Input: s = “???”

Output: “abc”

Explanation: In this example, we can replace the occurrences of '?' to make s equal to "abc".

For "abc", cost(0) = 0, cost(1) = 0, and cost(2) = 0.

The value of "abc" is 0.

Some other modifications of s that have a value of 0 are "cba", "abz", and, "hey".

Among all of them, we choose the lexicographically smallest.

Example 2:

Input: s = “a?a?”

Output: “abac”

Explanation: In this example, the occurrences of '?' can be replaced to make s equal to "abac".

For "abac", cost(0) = 0, cost(1) = 0, cost(2) = 1, and cost(3) = 0.

The value of "abac" is 1.

Constraints:

• 1 <= s.length <= 105
• s[i] is either a lowercase English letter or '?'.

Solution

public class Solution {
    public String minimizeStringValue(String s) {
        int n = s.length();
        int time = 0;
        int[] count = new int[26];
        int[] res = new int[26];
        char[] str = s.toCharArray();
        for (char c : str) {
            if (c != '?') {
                count[c - 'a']++;
            } else {
                time++;
            }
        }
        int minTime = Integer.MAX_VALUE;
        for (int i = 0; i < 26; i++) {
            minTime = Math.min(minTime, count[i]);
        }
        while (time > 0) {
            for (int j = 0; j < 26; j++) {
                if (count[j] == minTime) {
                    res[j]++;
                    count[j]++;
                    time--;
                }
                if (time == 0) {
                    break;
                }
            }
            minTime++;
        }
        int start = 0;
        for (int i = 0; i < n; i++) {
            if (str[i] == '?') {
                while (res[start] == 0) {
                    start++;
                }
                str[i] = (char) ('a' + start);
                res[start]--;
            }
        }
        return new String(str);
    }
}

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