LeetCode - Two Sum

http://blog.csdn.net/sunboy_2050/article/details/8783952

Summary：

1. vector<int> ret(2, 0);

   apply a vector: (size, initial value).

2. index starts from one (not zero).

3. small index comes first, big index comes next.

4. attention to the special condition:  input one element in vector.

5. <Algorithm> library:

　　sort(nums.begin(), nums.end(), compare);

　　bool compare(const& T1, const& T2){return ...}

　　min, max;

6. data structure: map<int, int>. (all 0 in default)

　　*use multiply as key, then judge the sum.

　　*attention to multiply-numbers, use "long long" type.

7. Java data structure:

　　HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();

　　map.containsKey(num);

　　map.put(num, index);

　　index = map.get(num);

 

　　

Others:

HashMap使用小结：http://blog.csdn.net/devillyd/article/details/3135479