Array - 数组问题

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1. Two Sum

已知数组 nums，求其中两数之和等于 target 的下标。

class Solution:
    def twoSum(self, nums: List[int], target: int) -> List[int]:
        all = dict()
        for x, y in enumerate(nums):
            if all.get(target - y, None) != None:
            # if target - y in all:  # 使用 in 简化逻辑
                return [all[target-y], x]
            else:
                all[y] = x

67. Add Binary

class Solution:
    def addBinary(self, a: str, b: str) -> str:
        length = max(len(a), len(b)) + 1
        a = '0' * (length - len(a)) + a
        b = '0' * (length - len(b)) + b
        ret = ''
        c = 0
        for i in range(length):
            s = int(a[-i-1]) + int(b[-i-1]) + c
            ret = str(s % 2) + ret
            c = s // 2
        if ret[0] == '0':
            return ret[1:]
        else:
            return ret