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Interpreter/main.cpp

+
+#include <iostream>
+#include <map>
+#include <stack>
+
+using namespace std;
+
+class Expression {
+public:
+    virtual int interpreter(map<char, int> var)=0;
+    virtual ~Expression(){}
+};
+
+//变量表达式
+class VarExpression: public Expression {
+    
+    char key;
+    
+public:
+    VarExpression(const char& key)
+    {
+        this->key = key;
+    }
+    
+    int interpreter(map<char, int> var) override {
+        return var[key];
+    }
+    
+};
+
+//符号表达式
+class SymbolExpression : public Expression {
+    
+    // 运算符左右两个参数
+protected:
+    Expression* left;
+    Expression* right;
+    
+public:
+    SymbolExpression( Expression* left,  Expression* right):
+        left(left),right(right){
+        
+    }
+    
+};
+
+//加法运算
+class AddExpression : public SymbolExpression {
+    
+public:
+    AddExpression(Expression* left, Expression* right):
+        SymbolExpression(left,right){
+        
+    }
+    int interpreter(map<char, int> var) override {
+        return left->interpreter(var) + right->interpreter(var);
+    }
+    
+};
+
+//减法运算
+class SubExpression : public SymbolExpression {
+    
+public:
+    SubExpression(Expression* left, Expression* right):
+        SymbolExpression(left,right){
+        
+    }
+    int interpreter(map<char, int> var) override {
+        return left->interpreter(var) - right->interpreter(var);
+    }
+    
+};
+
+
+
+Expression*  analyse(string expStr) {
+    
+    stack<Expression*> expStack;
+    Expression* left = nullptr;
+    Expression* right = nullptr;
+    for(int i=0; i<expStr.size(); i++)
+    {
+        switch(expStr[i])
+        {
+            case '+':
+                // 加法运算
+                left = expStack.top();
+                right = new VarExpression(expStr[++i]);
+                expStack.push(new AddExpression(left, right));
+                break;
+            case '-':
+                // 减法运算
+                left = expStack.top();
+                right = new VarExpression(expStr[++i]);
+                expStack.push(new SubExpression(left, right));
+                break;
+            default:
+                // 变量表达式
+                expStack.push(new VarExpression(expStr[i]));
+        }
+    }
+   
+    Expression* expression = expStack.top();
+
+    return expression;
+}
+
+void release(Expression* expression){
+    
+    //释放表达式树的节点内存...
+}
+
+int main(int argc, const char * argv[]) {
+    
+    
+    string expStr = "a+b-c+d-e";
+    map<char, int> var;
+    var.insert(make_pair('a',5));
+    var.insert(make_pair('b',2));
+    var.insert(make_pair('c',1));
+    var.insert(make_pair('d',6));
+    var.insert(make_pair('e',10));
+
+    
+    Expression* expression= analyse(expStr);
+    
+    int result=expression->interpreter(var);
+    
+    cout<<result<<endl;
+    
+    release(expression);
+    
+    return 0;
+}
+