leetcode 1

# 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].

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        lookup = {}
        for i, num in enumerate(nums):
            if target - num in lookup:
                return [lookup[target - num], i]
            lookup[num] = i #lookup里是由值查找索引
        return []


if __name__ == '__main__':
    print "index1=%d, index2=%d" % Solution().twoSum((2, 7, 11, 15), 9)

enumerate的用法：
遍历列表或者数组中的索引和元素。

def enumerate(collection):
  'Generates an indexed series:  (0,coll[0]), (1,coll[1]) ...'      
   i = 0
   it = iter(collection)
   while 1:
   yield (i, it.next())
   i += 1

enumerate会将数组或列表组成一个索引序列。使我们再获取索引和索引内容的时候更加方便如下：

for index，text in enumerate(list)):
   print index ,text

http://blog.csdn.net/xyw_blog/article/details/18401237