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class Solution {
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  int sum = 0;
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 public:
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  bool solve(TreeNode *root) {
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    if (root == NULL) return false;
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    if (root->left == NULL && root->right == NULL) return true;
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    if (solve(root->left)) sum += root->left->val;
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    solve(root->right);
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    return false;
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  }
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  int sumOfLeftLeaves(TreeNode *root) {
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    solve(root);
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    return sum;
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  }
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};