2053. Kth Distinct String in an Array

Description

A distinct string is a string that is present only once in an array.

Given an array of strings arr, and an integer k, return the kth distinct string present in arr. If there are fewer than k distinct strings, return an empty string "".

Note that the strings are considered in the order in which they appear in the array.

 

Example 1:

Input: arr = ["d","b","c","b","c","a"], k = 2
Output: "a"
Explanation:
The only distinct strings in arr are "d" and "a".
"d" appears 1st, so it is the 1st distinct string.
"a" appears 2nd, so it is the 2nd distinct string.
Since k == 2, "a" is returned. 

Example 2:

Input: arr = ["aaa","aa","a"], k = 1
Output: "aaa"
Explanation:
All strings in arr are distinct, so the 1st string "aaa" is returned.

Example 3:

Input: arr = ["a","b","a"], k = 3
Output: ""
Explanation:
The only distinct string is "b". Since there are fewer than 3 distinct strings, we return an empty string "".

 

Constraints:

• 1 <= k <= arr.length <= 1000
• 1 <= arr[i].length <= 5
• arr[i] consists of lowercase English letters.

Solutions

Solution 1: Hash Table + Counting

We can use a hash table $\textit{cnt}$ to record the number of occurrences of each string. Then, we traverse the array once more. For each string, if its occurrence count is $1$, we decrement $k$ by one. When $k$ reaches $0$, we return the current string.

Time complexity is $O(L)$, and space complexity is $O(L)$, where $L$ is the total length of all strings in the array $\textit{arr}$.

Python3JavaC++GoTypeScriptRustJavaScript

class Solution:
    def kthDistinct(self, arr: List[str], k: int) -> str:
        cnt = Counter(arr)
        for s in arr:
            if cnt[s] == 1:
                k -= 1
                if k == 0:
                    return s
        return ""

class Solution {
    public String kthDistinct(String[] arr, int k) {
        Map<String, Integer> cnt = new HashMap<>();
        for (String s : arr) {
            cnt.merge(s, 1, Integer::sum);
        }
        for (String s : arr) {
            if (cnt.get(s) == 1 && --k == 0) {
                return s;
            }
        }
        return "";
    }
}

class Solution {
public:
    string kthDistinct(vector<string>& arr, int k) {
        unordered_map<string, int> cnt;
        for (const auto& s : arr) {
            ++cnt[s];
        }
        for (const auto& s : arr) {
            if (cnt[s] == 1 && --k == 0) {
                return s;
            }
        }
        return "";
    }
};

func kthDistinct(arr []string, k int) string {
    cnt := map[string]int{}
    for _, s := range arr {
        cnt[s]++
    }
    for _, s := range arr {
        if cnt[s] == 1 {
            k--
            if k == 0 {
                return s
            }
        }
    }
    return ""
}

function kthDistinct(arr: string[], k: number): string {
    const cnt = new Map<string, number>();
    for (const s of arr) {
        cnt.set(s, (cnt.get(s) || 0) + 1);
    }
    for (const s of arr) {
        if (cnt.get(s) === 1 && --k === 0) {
            return s;
        }
    }
    return '';
}

use std::collections::HashMap;

impl Solution {
    pub fn kth_distinct(arr: Vec<String>, mut k: i32) -> String {
        let mut cnt = HashMap::new();

        for s in &arr {
            *cnt.entry(s).or_insert(0) += 1;
        }

        for s in &arr {
            if *cnt.get(s).unwrap() == 1 {
                k -= 1;
                if k == 0 {
                    return s.clone();
                }
            }
        }

        "".to_string()
    }
}

/**
 * @param {string[]} arr
 * @param {number} k
 * @return {string}
 */
var kthDistinct = function (arr, k) {
    const cnt = new Map();
    for (const s of arr) {
        cnt.set(s, (cnt.get(s) || 0) + 1);
    }
    for (const s of arr) {
        if (cnt.get(s) === 1 && --k === 0) {
            return s;
        }
    }
    return '';
};

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