[Google]find a,b,c such that a+b+c

Question:

Suppose you have a million integer numbers. 

Return all possible values of a,b and c such that 
a+b+c<=d. 
d will be provided to you. 
ex: if the numbers are 1,2,3,4,5,6,7 
and d=7 
[1,2,3] 
[1,2,4] 

[1,2,3] will be same as [1,3,2] and [3,2,1]... 

follow up: 

Return all such parts that satisfy the above condition if d is not provided.

Solution:

k-sum的问题一般有两种解法.

第一种:1)排序2)固定k-2个数位置3)两个指针分别从前往后和从后往前移动.

第二种:缓存k/2的数的和(和为key,数字为值),然后对剩余k/2个数遍历.

这题说到million,不知道有没有额外的技巧.望高人回答.