day 14.1: 227-basic-calculator-ii

227-basic-calculator-ii/driver.cpp

@@ -0,0 +1,10 @@
+#include "soln.hpp"
+
+int main()
+{
+	string s = "4+1-3*10/2*5";
+	int answer = -70;
+	Solution soln;
+	cout << "Evaluated expression correctly? " << soln.test(s, answer) << endl;
+	return 0;
+}

227-basic-calculator-ii/soln.cpp

@@ -0,0 +1,103 @@
+#include "soln.hpp"
+
+int Solution::calculate(string s)
+{
+	unordered_map<char, int> precedences{{'/', 2}, {'*', 2}, {'+', 1}, {'-', 1}};
+	int cur_int = 0;
+	vector<int> values;
+	vector<char> ops;
+	for (int i = 0; i < s.length(); i++)
+	{
+		char c = s[i];
+		if (c == ' ')
+			continue;
+		// digit, get the number (only positive nums)
+		if (isdigit(c))
+		{
+			cur_int = 0;
+			while (i < s.size() && isdigit(c))
+			{
+				cur_int *= 10;
+				cur_int += c - '0';
+				i++;
+				if (i == s.length())
+					break;
+				c = s[i];
+			}
+			i--;
+			values.push_back(cur_int);
+			cur_int = 0;
+		}
+		// operator
+		else
+		{
+			// if operator stack not empty
+			while (ops.empty() != true)
+			{
+				// new one is equal or lower, pop and perform old op first
+				if (precedences.at(ops.back()) >= precedences.at(c))
+				{
+					char op = ops.back();
+					ops.pop_back();
+					int val2 = values.back();
+					values.pop_back();
+					int val1 = values.back();
+					values.pop_back();
+					int result;
+					switch (op)
+					{
+					case '+':
+						result = val1 + val2;
+						break;
+					case '-':
+						result = val1 - val2;
+						break;
+					case '*':
+						result = val1 * val2;
+						break;
+					case '/':
+						result = val1 / val2;
+						break;
+					}
+					values.push_back(result);
+				}
+				else
+				{
+					break;
+				}
+			}
+			ops.push_back(c);
+		}
+	}
+	while (ops.empty() != true)
+	{
+		char op = ops.back();
+		ops.pop_back();
+		int val2 = values.back();
+		values.pop_back();
+		int val1 = values.back();
+		values.pop_back();
+		int result;
+		switch (op)
+		{
+		case '+':
+			result = val1 + val2;
+			break;
+		case '-':
+			result = val1 - val2;
+			break;
+		case '*':
+			result = val1 * val2;
+			break;
+		case '/':
+			result = val1 / val2;
+			break;
+		}
+		values.push_back(result);
+	}
+	return values[0];
+}
+
+bool Solution::test(string s, int answer)	{
+	return calculate(s) == answer;
+}

227-basic-calculator-ii/soln.hpp

@@ -0,0 +1,7 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution	{
+	public:
+    int calculate(string s);
+	bool test(string s, int answer);
+};