Python每日一练(20230422) 杨辉三角、最长回文子串、逆波兰表达式求值

from typing import List
class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        if numRows == 0:
            return []
        if numRows == 1:
            return [[1]]
        if numRows == 2:
            return [[1], [1, 1]]
        result = [[1], [1, 1]] + [[] for i in range(numRows - 2)]
        for i in range(2, numRows):
            for j in range(i + 1):
                if j == 0 or j == i:
                    result[i].append(1)
                else:
                    result[i].append(result[i - 1][j - 1] + result[i - 1][j])
        return result
if __name__ == "__main__":
    s = Solution()
    for i in range(1,6):
        print(s.generate(i))

class Solution:
    def longestPalindrome(self, s: str) -> str:
        ti = 0
        maxlen = 0
        i = 0
        while i < len(s):
            t = 1
            while t <= i and i + t < len(s):
                if s[i + t] == s[i - t]:
                    t += 1
                else:
                    break
            t -= 1
            if 2 * t + 1 > maxlen:
                ti = i - t
                maxlen = 2 * t + 1
            i += 1
        i = 0
        while i < len(s):
            t = 1
            while t <= i + 1 and i + t < len(s):
                if s[i - t + 1] == s[i + t]:
                    t += 1
                else:
                    break
            t -= 1
            if 2 * t > maxlen:
                ti = i - t + 1
                maxlen = 2 * t
            i += 1
        return s[ti:ti+maxlen]
# %%
s = Solution()
print(s.longestPalindrome('babad'))
print(s.longestPalindrome('cbbd'))

class Solution(object):
    def evalRPN(self, tokens):
        """
        :type tokens: List[str]
        :rtype: int
        """
        stack = []
        for token in tokens:
            if token not in ["+", "-", "*", "/"]:
                stack.append(int(token))
            else:
                num1 = stack.pop()
                num2 = stack.pop()
                if token == "+":
                    stack.append(num1 + num2)
                elif token == "-":
                    stack.append(num2 - num1)
                elif token == "*":
                    stack.append(num1 * num2)
                elif token == "/":
                    if num1 * num2 < 0:
                        result = -((-num2) // num1)
                        stack.append(result)
                    else:
                        stack.append(num2 // num1)
            #print(stack)
        return stack.pop()
# %%
s = Solution()
print(s.evalRPN(tokens = ["2","1","+","3","*"]))
print(s.evalRPN(tokens = ["4","13","5","/","+"]))
tokens = ["10","6","9","3","+","-11","*","/","*","17","+","5","+"]
print(s.evalRPN(tokens))