Jewels And Stones Problem


Description

LeetCode Problem 771. You’re given strings jewels representing the types of stones that are jewels, and stones representing the stones you have. Each character in stones is a type of stone you have. You want to know how many of the stones you have are also jewels.

Letters are case sensitive, so “a” is considered a different type of stone from “A”. Jewels and stones consist of only English letters.

Example 1:

1
2
Input: jewels = "aA", stones = "aAAbbbb"
Output: 3

Example 2:

1
2
Input: jewels = "z", stones = "ZZ"
Output: 0


Solution

When scanning through the jewels, we can use a hash table to store the jewels. Then for each stone, we check whether it matches any of the jewels.

To speed up the program, we can leverage the constraint that jewels and stones consist of only English letters. We can use an array instead of a hash table, and use the ASCII number of the letter as the index (instead of using the letter itself).

The time complexity is O(n + m), where n is the number of jewels and m is the number of stones. The space complexity is O(n).


Sample C++ Code

This is a C++ implementation of the above approach.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

int numJewelsInStones(string J, string S) {
    vector<int> ht(100, 0);
    for (int i = 0; i < J.size(); i ++) {
        ht[J[i]-'A'] = 1;
    }
    int cnt = 0;
    for (int i = 0; i < S.size(); i ++) {
        if (ht[S[i]-'A'] == 1)
            cnt ++;
    }
    return cnt;
}

int main() {
    string J = "aA";
    string S = "aAAbbbb";
    cout << numJewelsInStones(J, S) << endl;
}




Related Posts

Sum Of Unique Elements Problem

LeetCode 1748. You are given an integer array nums. The...

Insert Delete GetRandom O(1) Problem

LeetCode 380. Implement a RandomizedSet class.

N-Repeated Element In Size 2N Array Problem

LeetCode 961. In a array A of size 2N, there...

Intersection Of Two Arrays Problem

LeetCode 349. Given two arrays, write a function to compute...

Intersection Of Three Sorted Arrays Problem

LeetCode 1213. Given three integer arrays arr1, arr2 and arr3...