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###### tags: `Leetcode`

# 567. Permutation in String

###### Link : https://leetcode.com/problems/permutation-in-string/description/

## 題目
s1字串各種排列組合的子字串是否存在於s2字串中
## 程式碼

class Solution {
public:
    bool checkInclusion(string s1, string s2) {
        const int s1Size = s1.size(), s2Size = s2.size();
        if(s1Size > s2Size) return false;
        vector<int> s1Char(26, 0), temp(26, 0);
        //s1字元出現次數
        for(char &ch : s1)
            s1Char[ch - 'a']++;
        //s2中字元出現次數，先放入和s1大小相同的
        for(int i = 0;i < s1Size;i++)
            temp[s2[i] - 'a']++;//s2中字元出現次數
        
        for(int i = s1Size;i < s2Size;i++){
            //比較兩者出現次數是否相同
            if(s1Char == temp) 
                return true;
            //在s2中和s1長度相同的子字串向後移一位
            temp[s2[i] - 'a']++;
            temp[s2[i - s1Size] - 'a']--;
        }
        if(s1Char == temp) 
            return true;
        return false;
    }
};

## Date
### 2023/2/4