001-two-sum

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]

1. 方法一：时间复杂度O(n*n)

class solution(object):
        def twosum(self,nums,target):
                b =False
                i =0
                j =len(nums)-1
                while j>0:
                        while i
                                if not nums[i]+nums[j]==target :
                                        i +=1
                                else :
                                        b=True
                                        print( i+1,j+1)
                                        break
                            j-=1
                    if not b:
                        print("null")
sl=solution()
sl.twosum([1,3,7,8],10)

2. 方法二：网络转载（http://www.cnblogs.com/chruny/p/4788804.html）

class Solution(object):
    """
    :type nums: List[int]
    :type target: int
    :rtype: List[int]
    """

    def twosum(self,nums,target):
        b= False
        d ={}
        size = 0
        print(nums)

        while size < len(nums):
            if not int(nums[size]) in d:
                d[int(nums[size])]=size+1
            if target - int(nums[size]) in d:
                if d[target - int(nums[size])] < size+1:
                    b = True
                    ans = [d[target-int(nums[size])], size+1]
                    print(ans)

            size +=1
        if not b:
            print("null")

sl=Solution()
sl.twosum(nums=list(input("Please input a list: ")),target=int(input('And input a target:')))

3. 笔记：
   • len(nums): nums中键值对的数量
   • dictionary:字典的增删改(http://www.runoob.com/python/python-dictionary.html),
     键必须是唯一的，但值则不必。
     值可以取任何数据类型，但键必须是不可变的，如字符串，数字或元组

向字典添加新内容的方法是增加新的键/值对，修改或删除已有键/值对如下实例:

实例
dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'};
 
dict['Age'] = 8; # update existing entry
dict['School'] = "DPS School"; # Add new entry
print "dict['Age']: ", dict['Age'];
print "dict['School']: ", dict['School'];

• boolean:定义一个boolean变量,默认为false,在其他条件中定义为ture