383. Ransom letter

• Question no ： Power button 383
• Knowledge point ： Hash , Count
• Goal completion ：22/150
• summary
  stem ：
  

Ideas ：

• 1. Interpretation of the question ： Judge whether it can be used magazine The letters inside make up ransonNote, Letters cannot be reused
• 2. First of all, will magazine Build a dictionary with the letters and occurrences in str1
• 3. Then start traversing ransonNote Letters in , If you encounter magazine Letters not in , That is to say str1 Key values that do not exist in , Then return directly False
• 4. Each time from str1 Take out a letter from ransonNote when , take str1 The number of occurrences of the letter in is reduced by one , When str1 The number of occurrences of letters in is less than 0 when , explain magazine The letters in have been reused , return False

class Solution:
    def canConstruct(self, ransomNote: str, magazine: str) -> bool:
        str1 = {
    }
        str2 = {
    }
        for i in range(len(magazine)):
            if magazine[i] in str1:
                str1[magazine[i]] += 1
            else:
                str1[magazine[i]] = 1
        for j in range(len(ransomNote)):
            if ransomNote[j] in str1:
                str1[ransomNote[j]] -= 1
                if str1[ransomNote[j]] < 0:
                    return False
            else:
                return False
        return True