791. Custom Sort String

Description

order and str are strings composed of lowercase letters. In order, no letter occurs more than once.

order was sorted in some custom order previously. We want to permute the characters of str so that they match the order that order was sorted. More specifically, if x occurs before y in order, then x should occur before y in the returned string.

Return any permutation of str (as a string) that satisfies this property.

Constraints

• order has length at most 26, and no character is repeated in order.

• str has length at most 200.

• order and str consist of lowercase letters only.

Approach

Links

• Binarysearch

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input:

order = "cba"

str = "abcd"

Output: "cbad"

Explanation:

"a", "b", "c" appear in order, so the order of "a", "b", "c" should be "c", "b", and "a".

Since "d" does not appear in order, it can be at any position in the returned string. "dcba", "cdba", "cbda" are also valid outputs.

Solutions

Solution 1

/**
 * Time complexity : O(MAX(m, n)), where m & n is the length of order & str String
 * Space complexity : O(n)
 */

class Solution {
    public String customSortString(String order, String str) {
        int[] count = new int[26];
        for(char ch: str.toCharArray()) {
            count[ch-'a']++;
        }
        StringBuilder sb = new StringBuilder();
        for(char ch: order.toCharArray()) {
            while(count[ch-'a']-- > 0) {
                sb.append(ch);
            }
        }
        
        for(char ch = 'a'; ch <= 'z'; ch++) {
            while(count[ch-'a']-- > 0) {
                sb.append(ch);
            }
        }
        
        return sb.toString();
    }
}

Follow up