day 28: 155-min-stack, 150-evaluate-reverse-polish-notation

150-evaluate-reverse-polish-notation/driver.cpp

@@ -0,0 +1,10 @@
+#include "soln.hpp"
+
+int main()
+{
+	vector<string> tokens{"10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"};
+	int answer = 22;
+	Solution soln;
+	cout << "Evaluated postfix expression correctly? " << soln.test(tokens, answer) << endl;
+	return 0;
+}

150-evaluate-reverse-polish-notation/soln.cpp

@@ -0,0 +1,42 @@
+#include "soln.hpp"
+
+int Solution::evalRPN(vector<string> &tokens)
+{
+	vector<int> operands;
+	int a, b;
+	for (int i = 0; i < tokens.size(); i++)
+	{
+		if (tokens[i].length() > 1 || isdigit(tokens[i][0]))
+		{
+			operands.push_back(stoi(tokens[i]));
+		}
+		else
+		{
+			b = operands.back();
+			operands.pop_back();
+			a = operands.back();
+			operands.pop_back();
+			switch (tokens[i][0])
+			{
+			case '+':
+				operands.push_back(a + b);
+				break;
+			case '-':
+				operands.push_back(a - b);
+				break;
+			case '*':
+				operands.push_back(a * b);
+				break;
+			case '/':
+				operands.push_back(a / b);
+				break;
+			}
+		}
+	}
+	return operands[0];
+}
+
+bool Solution::test(vector<string> &tokens, int answer)
+{
+	return evalRPN(tokens) == answer;
+}

150-evaluate-reverse-polish-notation/soln.hpp

@@ -0,0 +1,8 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution
+{
+public:
+	int evalRPN(vector<string> &tokens);
+	bool test(vector<string> &tokens, int answer);
+};

155-min-stack/driver.cpp

@@ -0,0 +1,14 @@
+#include "soln.hpp"
+
+int main()
+{
+	MinStack *minStack = new MinStack();
+	minStack->push(-2);
+	minStack->push(0);
+	minStack->push(-3);
+	cout << minStack->getMin() << endl; // return -3
+	minStack->pop();
+	cout << minStack->top() << endl;	// return 0
+	cout << minStack->getMin() << endl; // return -2
+	return 0;
+}

155-min-stack/soln.cpp

@@ -0,0 +1,32 @@
+#include "soln.hpp"
+
+MinStack::MinStack()
+{
+	_stack = {};
+	total_min = INT_MAX;
+}
+
+void MinStack::push(int val)
+{
+	total_min = min(int(val), total_min);
+	_stack.push_back({val, total_min});
+}
+
+void MinStack::pop()
+{
+	_stack.pop_back();
+	if (_stack.size() == 0)
+		total_min = INT_MAX;
+	else
+		total_min = _stack.back().second;
+}
+
+int MinStack::top()
+{
+	return int(_stack.back().first);
+}
+
+int MinStack::getMin()
+{
+	return int(_stack.back().second);
+}

155-min-stack/soln.hpp

@@ -0,0 +1,15 @@
+#include <bits/stdc++.h>
+using namespace std;
+class MinStack
+{
+private:
+	vector<pair<int, int>> _stack;
+	int total_min;
+
+public:
+	MinStack();
+	void push(int val);
+	void pop();
+	int top();
+	int getMin();
+};