OJ Practice 48--t15 3Sum

Finding a column of integers and three numbers for 0 requires that the returned results be ordered sequentially and that the returned sequences differ from each other. For example:

Array S = {-1 0 1 2-1-4},
A Solution set is:
(-1, 0, 1) (-1,-1, 2)

Ideas

(It seems that I really do not have a bit of algorithmic mind)

For each current number, use the 2sum algorithm to find the remaining two numbers and the inverse number for the current number. 3sum degenerate into a 2sum problem.

Since the title does not require the return sequence ordinal, it can be used to sort the 2sum and then double-pointer traversal algorithm.

"Other Code"

vector<vector<int>> Threesum (vector<int>&num) {Vector<vector<int> >ret;        Ret.clear (); Sort (Num.begin (), Num.end ());//soga!!         for(intI=0; I!=num.size (); i++){            if(I >0&& num[i]==num[i-1])                Continue;//Duplicate triplets            intj,k; J=i+1; K=num.size ()-1;  while(j<k) {                if(j>i+1&&num[j]==num[j-1]) {J++; Continue; }                if(K<num.size ()-1&& num[k]==num[k+1]) {k--; Continue; }                 intsum = Num[i] + num[j] +Num[k]; if(sum>0) {k--; }Else if(sum<0) {J++; }Else{vector<int>tmp;                    Tmp.push_back (Num[i]);                    Tmp.push_back (Num[j]);                    Tmp.push_back (Num[k]);                    Ret.push_back (TMP); J++; }            }        }        returnret; } 

Summary

Because there are repeating numbers in the sequence, to remove duplicates, J and K are double-pointer searches.

It may be strange to do what happens if you omit the number of repetitions ( -1,-1,2).

So I debugged a bit by step = =

I point to-1, j=i+1, point to-1, so that you do not miss the three number of two numbers in the same situation. O (∩_∩) o~~

In addition, the STL's sort function should be a quick line, with the time O (Nlogn). The library function is very convenient, also thought to have to write manually ... Lazy cancer.

PostScript

Although the time spent a morning, but summed up the T1 2sum, read the beauty of Programming 2.12 section related explanations, or a little harvest.

OJ Practice 48--t15 3Sum