736

leetcode/hard/736.cc

@@ -0,0 +1,91 @@
+#include <iostream>
+#include <map>
+#include <queue>
+#include <string>
+#include <vector>
+
+using std::deque;
+using std::map;
+using std::string;
+using std::vector;
+
+using std::cout; using std::endl;
+
+class Solution {
+public:
+    int evaluate(string expression) {
+        int pos = 0;
+        return eval(expression, pos);
+    }
+
+private:
+    int eval(string exp, int& pos) {
+        int val = 0;
+        scopes.push_front(map<string, int>());
+        if (exp[pos] == '(') pos++;
+        string token = get_token(exp, pos);
+        if (token == "add") {
+            int val1 = eval(exp, ++pos);
+            int val2 = eval(exp, ++pos);
+            val = val1 + val2;
+        } else if (token == "mult") {
+            int val1 = eval(exp, ++pos);
+            int val2 = eval(exp, ++pos);
+            val = val1 * val2;
+        } else if (token == "let") {
+            vector<string> exps;
+            while (pos < exp.size() && exp[pos] == ' ')
+                exps.push_back(get_expression(exp, ++pos));
+            int j = 0;
+            for (int i = 0; i < exps.size() - 1; i += 2, j = 0) {
+                string var = exps[i];
+                int v = eval(exps[i + 1], j);
+                scopes.front()[var] = v;
+            }
+            val = eval(exps.back(), j);
+        } else if (isalpha(token[0])) {
+            val = find_value(token);
+        } else {
+            val = atoi(token.c_str());
+        }
+        if (pos < exp.size() && exp[pos] == ')') pos++;
+        scopes.pop_front();
+        return val;
+    }
+
+    string get_token(string exp, int& pos) {
+        int beg = pos;
+        while (exp[pos] != ' ' && exp[pos] != ')') pos++;
+        return exp.substr(beg, pos - beg);
+    }
+
+    string get_expression(string exp, int& pos) {
+        int beg = pos, cnt = 0;
+        while (pos < exp.size() && (cnt != 0 || (exp[pos] != ' ' && exp[pos] != ')'))) {
+            char c = exp[pos++];
+            if (c == '(') cnt++;
+            if (c == ')') cnt--;
+        }
+        return exp.substr(beg, pos - beg);
+    }
+
+    int find_value(string token) {
+        for (auto it = scopes.cbegin(); it != scopes.cend(); ++it)
+            if (it->count(token))
+                return it->at(token);
+        return 0;
+    }
+
+    deque<map<string, int>> scopes;
+};
+
+// (add 1 (let x 2 x))
+
+int main() {
+    Solution* sol = new Solution();
+
+    cout << sol->evaluate("mult (add (add 1 3) 4) 5") << endl;
+    cout << sol->evaluate("let x 3 y 9 x 1 x 4 (add x (let x 2 (add (add 1 x) 4)))") << endl;
+
+    return 0;
+}