771. Jewels and Stones

 

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

The letters in J are guaranteed distinct, and all characters in J and S are letters. Letters are case sensitive, so "a" is considered a different type of stone from "A".

Example 1:

Input: J = "aA", S = "aAAbbbb"
Output: 3

Example 2:

Input: J = "z", S = "ZZ"
Output: 0

Note:

  • S and J will consist of letters and have length at most 50.
  • The characters in J are distinct.

 

这道题给了我们两个字符串,珠宝字符串J和石头字符串S,其中J中的每个字符都是珠宝,S中的每个字符都是石头,问我们S中有多少个珠宝。这道题没什么难度,高于八成的Accept率也应证了其Easy难度实至名归。那么先来暴力搜索吧,就将S中的每个字符都在J中搜索一遍,搜索到了就break掉,参见代码如下:

 

解法一:

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        int res = 0;
        for (char s : S) {
            for (char j : J) {
                if (s == j) {
                    ++res; break;
                }
            }
        }
        return res;
    }
};

 

我们用HashSet来优化时间复杂度,将珠宝字符串J中的所有字符都放入HashSet中,然后遍历石头字符串中的每个字符,到HashSet中查找是否存在,存在的话计数器自增1即可,参见代码如下:

 

解法二:

class Solution {
public:
    int numJewelsInStones(string J, string S) {
        int res = 0;
        unordered_set<char> s;
        for (char c : J) s.insert(c);
        for (char c : S) {
            if (s.count(c)) ++res;
        }
        return res;
    }
};

 

参考资料:

https://leetcode.com/problems/jewels-and-stones/solution/

https://leetcode.com/problems/jewels-and-stones/discuss/113553/C++JavaPython-Easy-and-Concise-Solution-O(M+N)

 

LeetCode All in One 题目讲解汇总(持续更新中…)


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