242.有效的字母异位词

https://leetcode.cn/problems/valid-anagram/description/

class Solution {
public:
    bool isAnagram(string s, string t) {
        if(s.size()!=t.size())
        return false;

        int hash[26] = {0};
        for(int i = 0; i < s.size(); i++)
        {
            hash[s[i] - 'a']++;
        }
        for(int i = 0; i < s.size(); i++)
        {
            hash[t[i] - 'a']--;
        }
        for(int i = 0; i < 26; i++)
        {
            if(hash[i]!=0)
            return false;
        }
        return true;
    }
};

349. 两个数组的交集

https://leetcode.cn/problems/intersection-of-two-arrays/description/

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> res;
        unordered_set<int> nums(nums1.begin(),nums1.end());//把nums1全添加进来
        for(int num : nums2)                               //遍历nums2数组
        {
            //nums2的元素在nums1里(也就是nums)出现过
            if(nums.find(num) != nums.end())
            res.insert(num);
        }
        return vector<int> (res.begin(),res.end());
    }
};

383. 赎金信

https://leetcode.cn/problems/ransom-note/

class Solution {
public:
    bool canConstruct(string ransomNote, string magazine) {
        int len1 = ransomNote.size();
        int len2 = magazine.size();
        if(len1 > len2)
        return false;

        int hash[26] = {0};
        for(int i = 0; i < len2; i++)
        {
            hash[magazine[i]-'a']++;
        }
        for(int i = 0; i < len1; i++)
        {
            hash[ransomNote[i]-'a']--;
        }
        
        for(int i = 0; i < 26; i++)
        {
            if(hash[i] < 0)
            return false;
        }
        return true;
    }
};

49.字母异位词分组

https://leetcode.cn/problems/group-anagrams/description/

class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        //对所有的string排序，比如bac cba cab 排完序后都是abc, 于是可以用map, abc就是索引, value值就是bac cba cab
        unordered_map<string,vector<string>> mp;
        for(string s : strs) //表示遍历strs的所有string, 这个str是入参
        {
            string cur = s;          //用于记录cur,因为排序完之后就变了
            sort(s.begin(),s.end()); //bac->abc 
            mp[s].push_back(cur);
        }
        vector<vector<string>> res;
        for(auto vs : mp)//一次推入一个vector<string>
        res.push_back(vs.second);
        return res;
    }
};

438.找到字符串中的所有字母异位词

https://leetcode.cn/problems/find-all-anagrams-in-a-string/description/

class Solution {
public:
    vector<int> findAnagrams(string s, string p) {
        int m = p.size();
        if(m > s.size())return {};

        vector<int> res;
        vector<int> hashs(26),hashp(26);
        for(int i = 0; i < m; i++)
        {
            hashp[p[i]-'a']++;
            hashs[s[i]-'a']++;
        }
        //此刻的hashp[]就是记录了abc有一个a 一个b 一个c
        if(hashp == hashs)
        res.push_back(0);
        for(int i = m; i < s.size(); i++)
        {
            //滑动窗口，右边的加进来，左边的滑出去
            hashs[s[i]-'a']++;
            hashs[s[i-m]-'a']--;

            if(hashp == hashs)
            res.push_back(i-m+1);
        }
        return res;
    }
};

349.两个数组的交集

https://leetcode.cn/problems/intersection-of-two-arrays/

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        unordered_set<int> res;
        unordered_set<int> nums(nums1.begin(),nums1.end());//把nums1全添加进来
        for(int num : nums2)                               //遍历nums2数组
        {
            //nums2的元素在nums1里(也就是nums)出现过
            if(nums.find(num) != nums.end())
            res.insert(num);
        }
        return vector<int> (res.begin(),res.end());
    }
};