leetcode 167. Two Sum II - Input array is sorted( Python )

描述

Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2.

Note:

Your returned answers (both index1 and index2) are not zero-based.
You may assume that each input would have exactly one solution and you may not use the same element twice.
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Example:

Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.
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解析

根據字典的特性，在遍歷 numbers 的時候，查看是否有符合結果的兩個數字，有的話直接返回索引結果，不然就將其加入字典中，時間複雜度爲 O(N)，空間複雜度爲 O(N)。

解答

class Solution(object):
    def twoSum(self, numbers, target):
        """
        :type numbers: List[int]
        :type target: int
        :rtype: List[int]
        """
        d = {}
        for i in range(len(numbers)):
            if target - numbers[i] in d:
                return [ d[target - numbers[i]],i+1 ]
            elif numbers[i] not in d:
                d[numbers[i]] = i+1
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運行結果

Runtime: 48 ms, faster than 81.07% of Python online submissions for Two Sum II - Input array is sorted.
Memory Usage: 12.5 MB, less than 7.71% of Python online submissions for Two Sum II - Input array is sorted.
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