fenghaolw

Given an index  k , return the  k th  row of the Pascal's triangle. For example, given  k  = 3, Return  [1,3,3,1] . Note: Could you optimize your algorithm to use only  O ( k ) extra space? Solution: This one is easy. If we modify the previous array instead of creating a new array, we only need O(k) extra space. The following code passes the LeetCode Online Large Judge.

Given  numRows , generate the first  numRows  of Pascal's triangle. For example, given  numRows  = 5, Return [ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6,4,1] ] Solution: This one is easy. The following code passes LeetCode Online Large Judge. Redo it at Aug. 24, 2013. BUG free.

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases. For example, "A man, a plan, a canal: Panama"  is a palindrome. "race a car"  is  not  a palindrome. Note: Have you consider that the string might be empty? This is a good question to ask during an interview. For the purpose of this problem, we define empty string as valid palindrome. Solution: This one is easy. The following code passes LeetCode Online Large Judge. Redo it at Sep. 8, bug free JAVA version:

The gray code is a binary numeral system where two successive values differ in only one bit. Given a non-negative integer  n  representing the total number of bits in the code, print the sequence of gray code. A gray code sequence must begin with 0. For example, given  n  = 2, return  [0,1,3,2] . Its gray code sequence is: 00 - 0 01 - 1 11 - 3 10 - 2 Note: For a given  n , a gray code sequence is not uniquely defined. For example,  [0,2,3,1]  is also a valid gray code sequence according to the above definition. Solution: There is a good instruction on  Wiki  about how to generate a gray code recursively. The following code passes LeetCode Online Large Judge. Update: Thank Yao for providing a much neater version Update: my own solution when I redo this problem (2013.05.17). NO RECURSION AND BUG FREE!

Given an integer, convert it to a roman numeral. Input is guaranteed to be within the range from 1 to 3999. Solution: This problem is simple. Just need to check  wiki  to understand how to represent a roman number... Still get bug-free after almost one month break, hooray :) The following code passes LeetCode Online Large Judge.