关于二叉树的一道面试题

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刚看到一个题：

给一个string of nested ternary operations例如a?b?c:d:e，build a tree：root是a，左子树是b?c:d对应的tree ，右子树是e。保证input都是valid的。

嗯，先给自己挖个坑，暂时没空，先放着，感兴趣的也可以自己做一做（2015/1/27）

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今天来把这个坑填上。（2015/2/3）

我假设a,b等就是单个字符。如果不是的话，那需要修改代码才行。

class Expression{public:Expression(string str):input(str),currpos(0) {}TreeNode *parse() const;bool match(char c) const { if (input[currpos] == c) {currpos++; return true;}  return false;}char readChar() const { return input[currpos++];}void print(TreeNode* pTree);void delTree(TreeNode* ptree);private:mutable int currpos;string input;};TreeNode* Expression::parse() const{TreeNode* pNode = NULL;char c = readChar();if (c == '\0') {return pNode;}pNode = new TreeNode(c);if (match('?')) {TreeNode* pLeft = parse();pNode->left = pLeft;} else {return pNode;}match(':');TreeNode* pRight = parse();pNode->right = pRight;return pNode;}void Expression::print(TreeNode* pTree){if (pTree == NULL)return;cout << pTree->val;if (pTree->left != NULL) {cout << '?';print(pTree->left);}if (pTree->right != NULL) {cout << ':';print(pTree->right);}}void Expression::delTree(TreeNode* ptree){if (ptree == NULL)return;delTree(ptree->left);delTree(ptree->right);delete ptree;}

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