Find Words That Can Be Formed by Characters LeetCode solution in C++

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class Solution {
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 public:
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  int countCharacters(vector<string> &words, string chars) {
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    vector<int> dp(26, 0);
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    vector<int> dp2(26, 0);
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    for (int i = 0; i < chars.size(); i++) {
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      dp[chars[i] - 'a']++;
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    }
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    dp2 = dp;
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    bool flg = false;
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    int cnt = 0;
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    for (int i = 0; i < words.size(); i++) {
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      string a = words[i];
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      for (int j = 0; j < a.size(); j++) {
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        if (dp[a[j] - 'a'] > 0) {
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          dp[a[j] - 'a']--;
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        } else {
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          flg = true;
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          dp = dp2;
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          break;
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        }
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      }
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      if (!flg) {
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        cnt += a.size();
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      }
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      dp = dp2;
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      flg = false;
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    }
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    return cnt;
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  }
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};