1.两数之和.py

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# @lc app=leetcode.cn id=1 lang=python
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# [1] 两数之和
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# https://leetcode-cn.com/problems/two-sum/description/
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# algorithms
# Easy (45.61%)
# Total Accepted:    318.5K
# Total Submissions: 698.3K
# Testcase Example:  '[2,7,11,15]\n9'
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# 给定一个整数数组 nums 和一个目标值 target，请你在该数组中找出和为目标值的那 两个 整数，并返回他们的数组下标。
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# 你可以假设每种输入只会对应一个答案。但是，你不能重复利用这个数组中同样的元素。
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# 示例:
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# 给定 nums = [2, 7, 11, 15], target = 9
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# 因为 nums[0] + nums[1] = 2 + 7 = 9
# 所以返回 [0, 1]
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# 
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class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        map = {}
        for i,num in enumerate(nums):
            a = target-num
            if a in map:
                return [map[a],i]
            map[num] = i
        return None