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class Solution {
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 public:
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  bool sumGame(string num) {
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    const int N = num.length();
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    int lDigitSum = 0;
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    int lQCount = 0;
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    int rDigitSum = 0;
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    int rQCount = 0;
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    for (int i = 0; i < N; ++i) {
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      if (isdigit(num[i])) {
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        if (i < N / 2) {
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          lDigitSum += (num[i] - '0');
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        } else {
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          rDigitSum += (num[i] - '0');
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        }
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      } else {
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        if (i < N / 2) {
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          ++lQCount;
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        } else {
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          ++rQCount;
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        }
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      }
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    }
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    // Case 0: Only digits (without '?')
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    if ((lQCount + rQCount) == 0) {
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      return (lDigitSum != rDigitSum);
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    }
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    // Case 1: Odd number of '?'
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    if ((lQCount + rQCount) % 2 == 1) {
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      return true;
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    }
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    // Case 2: Even number of '?'
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    int minQCount = min(lQCount, rQCount);
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    lQCount -= minQCount;
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    rQCount -= minQCount;
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    return (lDigitSum + 9 * lQCount / 2 != rDigitSum + 9 * rQCount / 2);
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  }
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};