Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9, return [0, 1].

Solution

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class Solution:
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        
        # Solution A:
        # for a in range(len(nums)):
        #     for b in range(a+1, len(nums)):
        #         if nums[a] + nums[b] == target:
        #             return [a, b]

        # Solution B:
        # map = {}
        # for i in range(len(nums)):
        #     map[nums[i]] = i

        # for i in range(len(nums)):
        #     complement = target - nums[i]
        #     if complement in map and map[complement] != i:
        #         return [i, map[complement]]

        # Solution C:
        map = {}
        for i in range(len(nums)):
            complement = target - nums[i]
            if complement in map:
                return [i, map[complement]]
            map[nums[i]] = i

字典的查找原来这么快。