我是C ++的新手，并使用调车场算法来构建表达式树。我已经坚持了几天这个问题。我试图获取根节点的值但它失败了。
中缀输入
(1+2)*(3/4)-(5+6)
以下代码是基于shungting码的功能：
vector<string> infixToRPN(vector<string> tokens) {
vector<string> output;
stack<string> stack;
string o1;
string o2;
//traverse tokens
for (int i = 0; i < tokens.size(); ++i) {
// if token is operator
if (isOperator(tokens[i])) {
string o1 = tokens[i];
if (!stack.empty()) {
string o2 = stack.top();
while (isOperator(o2) && comparePrecendence(o1, o2) <= 0) {
// pop off o2 and on to the output;
stack.pop();
output.push_back(o2);
if (!stack.empty())
o2 = stack.top();
else
break;
}
}
//push o1 on to the stack;
stack.push(o1);
}
//if token is left bracket
else if (tokens[i] == "(") {
stack.push(tokens[i]);
}
//if token is right bracket
else if (tokens[i] == ")") {
string topToken = stack.top();
while (stack.top() != "(") {
output.push_back(topToken);
stack.pop();
if (stack.empty()) break;
topToken = stack.top();
}
if (!stack.empty()) stack.pop();
}
// if token is number and add it to ouput;
else
{
output.push_back(tokens[i]);
}
}
//pop the rest of token
while (!stack.empty()) {
string restToken = stack.top();
output.push_back(restToken);
stack.pop();
}
return output;
}
测试结果表明解析器似乎正常工作：
12+34/*56+-
所以我猜错误可能发生在我的buildTree函数中。在buiilding之后，getRoot（）函数返回的值总是与正确的值不一致。在我的情况下，根应该是“ - ”，而我得到一个“0”。
ExprTree ExprTree::buildTree(vector<string> tokens){
ExprTree t ;
TreeNode * n, * n1, * n2;
TreeNode * r = t.getRoot();
vector<string> postfix = infixToRPN(tokens);
stack<TreeNode *> stack;
for (int i = 0; i < postfix.size(); ++i) {
//if number
if (!isOperator(postfix[i])) {
n = createOperatorNode(postfix[i]);
stack.push(n);
}
else // if operator
{
n= createOperatorNode(postfix[i]);
if (!stack.empty())
t = ExprTree(stack.top());
// pop two tree nodes
n1 = stack.top();
stack.pop();
n2 = stack.top();
stack.pop();
//set children nodes;
n->setLeftChild(n2);
n->setRightChild(n1);
stack.push(n);
}
}
return t;
}