LC Hashtable

简单

242. 有效的字母异位词

def isAnagram(self, s,t):
	s_map,t_map = {},{}
	for c in s:
		if c in s_map:
			s_map[c] += 1
		else:
			s_map[c] = 1
	for c in t:
		if c in t_map:
			t_map[c] += 1
		else:
			t_map[c] = 1
	return s_map == t_map

中等

15. 三数之和：

def threeSum(self, nums):
	#Method1 dfs
	nums.sort()
    res = []
    def dfs(first,cur,cumsum):
        if len(cur)==3 and cumsum == 0:
            res.append(cur)
        for i in range(first,len(nums)):
            if i>first and nums[i]==nums[i-1]: continue
            if cumsum+nums[i]>0: return 
            dfs(i+1,cur+[nums[i]],cumsum+nums[i])
    dfs(0,[],0)
    return res
    #Method2 hashtable
    nums.sort()
    res,d = set(),{}
    if len(nums)<3:
        return []
    for i,v in enumerate(nums):
        if v not in d:
            d[v] = [i]
        else:
            d[v].append(i)
    for i in range(0,len(nums)):
        for j in range(i+1,len(nums)):
            if -nums[i]-nums[j] in d:
                ll = d[-nums[i]-nums[j]]
                for x in ll:
                    if x!= i and x!=j:
                    	res.add(tuple(sorted([nums[i],nums[j],-nums[i]-nums[j]])))
        res = [list(x) for x in res]
    return res
    			

困难