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feat: add solutions to lcof2 problem: No.036 Evaluate Reverse Polish Notation
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‎lcof2/剑指 Offer II 036. 后缀表达式/README.md

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<!-- 这里可写通用的实现逻辑 -->
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利用栈存储运算数，每次遇到符号，对栈顶两个元素进行运算
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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需要注意 Python 的整除对负数也是向下取整（例如：`6 // -132 = -1`），和答案对应不上，所以需要特殊处理
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```python
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class Solution:
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def evalRPN(self, tokens: List[str]) -> int:
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nums = []
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for t in tokens:
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if len(t) > 1 or t.isdigit():
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nums.append(int(t))
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else:
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if t == "+":
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nums[-2] += nums[-1]
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elif t == "-":
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nums[-2] -= nums[-1]
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elif t == "*":
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nums[-2] *= nums[-1]
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else:
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nums[-2] = int(nums[-2] / nums[-1])
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nums.pop()
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return nums[0]
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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public int evalRPN(String[] tokens) {
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Deque<Integer> stack = new ArrayDeque<>();
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for (String t : tokens) {
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if (t.length() > 1 || Character.isDigit(t.charAt(0))) {
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stack.push(Integer.parseInt(t));
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} else {
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int y = stack.pop();
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int x = stack.pop();
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switch (t) {
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case "+":
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stack.push(x + y);
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break;
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case "-":
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stack.push(x - y);
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break;
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case "*":
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stack.push(x * y);
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break;
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default:
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stack.push(x / y);
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break;
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}
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}
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}
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return stack.pop();
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}
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}
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```
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### **Go**
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```go
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func evalRPN(tokens []string) int {
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// https://github.com/emirpasic/gods#arraystack
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stack := arraystack.New()
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for _, token := range tokens {
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if len(token) > 1 || token[0] >= '0' && token[0] <= '9' {
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num, _ := strconv.Atoi(token)
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stack.Push(num)
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} else {
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y := popInt(stack)
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x := popInt(stack)
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switch token {
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case "+":
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stack.Push(x + y)
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case "-":
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stack.Push(x - y)
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case "*":
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stack.Push(x * y)
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default:
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stack.Push(x / y)
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}
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}
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}
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return popInt(stack)
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}
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func popInt(stack *arraystack.Stack) int {
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v, _ := stack.Pop()
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return v.(int)
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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int evalRPN(vector<string>& tokens) {
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stack<int> stk;
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for (const auto& token : tokens) {
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if (token.size() > 1 || isdigit(token[0])) {
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stk.push(stoi(token));
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} else {
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int y = stk.top();
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stk.pop();
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int x = stk.top();
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stk.pop();
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if (token[0] == '+') stk.push(x + y);
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else if (token[0] == '-') stk.push(x - y);
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else if (token[0] == '*') stk.push(x * y);
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else stk.push(x / y);
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}
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}
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return stk.top();
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}
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};
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```
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### **...**

‎lcof2/剑指 Offer II 036. 后缀表达式/Solution.cpp

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class Solution {
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public:
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int evalRPN(vector<string>& tokens) {
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stack<int> stk;
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for (const auto& token : tokens) {
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if (token.size() > 1 || isdigit(token[0])) {
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stk.push(stoi(token));
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} else {
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int y = stk.top();
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stk.pop();
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int x = stk.top();
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stk.pop();
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if (token[0] == '+') stk.push(x + y);
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else if (token[0] == '-') stk.push(x - y);
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else if (token[0] == '*') stk.push(x * y);
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else stk.push(x / y);
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}
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}
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return stk.top();
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}
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};

‎lcof2/剑指 Offer II 036. 后缀表达式/Solution.go

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func evalRPN(tokens []string) int {
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// https://github.com/emirpasic/gods#arraystack
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stack := arraystack.New()
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for _, token := range tokens {
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if len(token) > 1 || token[0] >= '0' && token[0] <= '9' {
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num, _ := strconv.Atoi(token)
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stack.Push(num)
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} else {
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y := popInt(stack)
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x := popInt(stack)
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switch token {
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case "+":
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stack.Push(x + y)
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case "-":
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stack.Push(x - y)
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case "*":
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stack.Push(x * y)
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default:
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stack.Push(x / y)
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}
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}
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}
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return popInt(stack)
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}
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func popInt(stack *arraystack.Stack) int {
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v, _ := stack.Pop()
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return v.(int)
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}

‎lcof2/剑指 Offer II 036. 后缀表达式/Solution.java

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class Solution {
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public int evalRPN(String[] tokens) {
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Deque<Integer> stack = new ArrayDeque<>();
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for (String t : tokens) {
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if (t.length() > 1 || Character.isDigit(t.charAt(0))) {
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stack.push(Integer.parseInt(t));
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} else {
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int y = stack.pop();
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int x = stack.pop();
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switch (t) {
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case "+":
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stack.push(x + y);
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break;
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case "-":
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stack.push(x - y);
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break;
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case "*":
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stack.push(x * y);
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break;
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default:
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stack.push(x / y);
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break;
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}
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}
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}
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return stack.pop();
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}
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}

‎lcof2/剑指 Offer II 036. 后缀表达式/Solution.py

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class Solution:
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def evalRPN(self, tokens: List[str]) -> int:
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nums = []
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for t in tokens:
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if len(t) > 1 or t.isdigit():
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nums.append(int(t))
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else:
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if t == "+":
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nums[-2] += nums[-1]
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elif t == "-":
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nums[-2] -= nums[-1]
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elif t == "*":
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nums[-2] *= nums[-1]
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else:
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nums[-2] = int(nums[-2] / nums[-1])
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nums.pop()
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return nums[0]

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