1. Two Sum

1. Two Sum

Leetcode link for this question

Discription:

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.

Example:

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

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

UPDATE (2016/2/13):
The return format had been changed to zero-based indices. Please read the above updated description carefully.

Analyze:

Code 1 （exhaustive search）:

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        for i in range(len(nums)):
            for j in range(i+1,len(nums)):
                if nums[i]+nums[j]==target:
                    return[i,j]

Submission Result:

Status: Accepted
Runtime: 5872 ms
Ranking: beats 9.41%

Code 2:

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        tmp=[]
        for i in range(len(nums)):
            tmp.append((i,nums[i]))
        tmp=sorted(tmp,key=lambda t:t[1]) ###  use tuple to sort nums and get the index
        nums.sort()
        i=0
        j=len(nums)-1        
        while i<=j:
            if nums[i]+nums[j]<target:
                i+=1
            elif nums[i]+nums[j]>target:
                j-=1
            else:
                return [tmp[i][0],tmp[j][0]]

Submission Result:

Status: Accepted
Runtime: 52 ms
Ranking: beats 73.69%