feat(work): add solutions for 150.evaluate-reverse-polish-notation and 155.min-stack, remove 42.trapping-rain-water

2026-09-17 07:26:27 +00:00 · 2026-08-27 15:21:16 -04:00
parent 53136b076c
commit 9b5879b6eb
3 changed files with 174 additions and 44 deletions
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+"""
+150. Evaluate Reverse Polish Notation
+Difficulty: Medium
+https://leetcode.com/problems/evaluate-reverse-polish-notation/
+
+──────────────────────────────────────────────────
+
+You are given an array of strings tokens that represents an
+arithmetic expression in a Reverse Polish Notation.
+
+Evaluate the expression. Return an integer that represents the value
+of the expression.
+
+Note that:
+
+        • The valid operators are '+', '-', '*', and '/'.
+
+        • Each operand may be an integer or another expression.
+
+        • The division between two integers always truncates toward zero.
+
+        • There will not be any division by zero.
+
+• The input represents a valid arithmetic expression in a reverse
+polish notation.
+
+• The answer and all the intermediate calculations can be
+represented in a 32-bit integer.
+
+
+
+Example 1:
+
+Input: tokens = ["2","1","+","3","*"]
+Output: 9
+Explanation: ((2 + 1) * 3) = 9
+
+Example 2:
+
+Input: tokens = ["4","13","5","/","+"]
+Output: 6
+Explanation: (4 + (13 / 5)) = 6
+
+Example 3:
+
+Input: tokens =
+["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
+Output: 22
+Explanation: ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
+= ((10 * (6 / (12 * -11))) + 17) + 5
+= ((10 * (6 / -132)) + 17) + 5
+= ((10 * 0) + 17) + 5
+= (0 + 17) + 5
+= 17 + 5
+= 22
+
+
+
+Constraints:
+
+        • 1 <= tokens.length <= 10^4
+
+• tokens[i] is either an operator: "+", "-", "*", or "/", or an
+integer in the range [-200, 200].
+"""
+
+
+class Solution:
+    def evalRPN(self, tokens: List[str]) -> int:
+        stack = []
+        operations = {
+            "+": lambda x, y: int(x + y),
+            "-": lambda x, y: int(x - y),
+            "*": lambda x, y: int(x * y),
+            "/": lambda x, y: int(x / y),
+        }
+
+        for c in tokens:
+            if c in operations:
+                y = stack.pop()
+                x = stack.pop()
+                calc_func = operations[c]
+                result = calc_func(x, y)
+                stack.append(result)
+            else:
+                stack.append(int(c))
+
+        return stack[0]