xmind: update links algorithm
leetcode: make a clear solution for swap-nodes-in-pairs
xmind: update algorithms of quick sort
leetcode: sort-colors
xmind: update algorithms
leetcode: linked list cycle. fast and slow ptr
leetcode: n-queens.. do some tricks inside.
leetcode: plus-one in digit list
leetcode: rotate-image, just swap 1/4
leetcode: search a 2d matrix.. easy one
leetcode: set matrix to zeros, hard to make it in-place