leetcode -- Longest Consecutive Sequence -- 重点

https://leetcode.com/problems/longest-consecutive-sequence/

思路很简单。看http://www.cnblogs.com/zuoyuan/p/3765546.html
http://chaoren.is-programmer.com/posts/42924.html

code

class Solution(object):
    def longestConsecutive(self, num):
        """ :type nums: List[int] :rtype: int """
        dict = {x:False for x in num} # False means not visited
        maxLen = -1
        for i in dict:
            if dict[i] == False:
                curr = i + 1; len1 = 0
                while curr in dict and dict[curr] == False:
                    len1 += 1; dict[curr] = True; curr += 1
                curr = i - 1; len2 = 0
                while curr in dict and dict[curr] == False:
                    len2 += 1; dict[curr] = True; curr -= 1
                maxLen = max(maxLen, 1 + len1 + len2)
        return maxLen

自己重做

可以AC，但是这里没必要使用count。只用flag就行

class Solution(object):
    def longestConsecutive(self, nums):
        """ :type nums: List[int] :rtype: int """
        if len(nums) == 0: return 0
        flag = {}
        count = {}
        for x in nums:
            if x not in flag: flag[x] = False
            if x in count:
                count[x] += 1
            else:
                count[x] = 1

        res = 0
        for x in nums:

            if not flag[x]:

                flag[x] = True
                cur = x; sub_count = 0;
                for i in xrange(1, len(nums)):
                    cur = x + i
                    if cur in count:
                        flag[cur] = True
                        sub_count += 1
                    else:
                        break
                cur = x
                for i in xrange(1, len(nums)):
                    cur = x - i
                    if cur in count:
                        flag[cur] = True
                        sub_count += 1
                    else:
                        break
                sub_count += 1
                res = max(res, sub_count)
        return res

另一个更简单的AC code

class Solution(object):
    def longestConsecutive(self, nums):
        """ :type nums: List[int] :rtype: int """
        if len(nums) == 0: return 0
        flag = { x:False for x in nums}#注意这里flag list comprehension的方法
        res = 0
        for x in nums:

            if not flag[x]:
                flag[x] = True
                cur = x + 1
                len1 = 0
                while cur in flag and flag[cur] == False:
                    len1 += 1
                    flag[cur] = True#注意这个flag 要在cur += 1之前。
                    cur += 1

                cur = x - 1
                len2 = 0
                while cur in flag and flag[cur] == False:
                    len2 += 1
                    flag[cur] = True#注意这个flag 要在cur -= 1之前。
                    cur -= 1
                #print len1, len2
                res = max(res, len1 + len2 + 1)
        return res