Ref: https://leetcode.com/problems/binary-search-tree-iterator/

First Thought

I decided to put the majority of the functions in hasNext() , if we want to iterate through the binary search tree, we need a in-order…

Ref: https://leetcode.com/problems/3sum-closest/

First Thought

3Sum is a variation of 2Sum Closest, if we sort the array first, then iterate through all the numbers, chose 2Sum closest in the rest of the array, we can get all the combinations…

Ref: https://leetcode.com/problems/number-of-distinct-islands
Ref: https://lintcode.com/problem/number-of-distinct-islands

First Thought

Ref: https://leetcode.com/problems/coin-change-2/

First Thought

The difference between Coin Change and this question is that the previous question wants a combination with least amount of coins while in this question we want all the combination…

Ref: https://leetcode.com/problems/permutations-ii/

First Thought

Compared with Permutation, the key for Permutation II is that because we select one digit at a time, we want to skip all candidates same with the current one after we made…