public class Solution { public boolean validUtf8(int[] data) { int count=0; for(int d : data){ if(count==0){ if((d>>3)==0b11110) count=3; else if((d>>4)==0b1110) count=2; else if((d>>5)==0b110) count=1; else if((d>>7)==0b1) return false; } else { if((d>>6)!=0b10) return false; count--; } } return count==0; } }

We are playing the Guess Game. The game is as follows: I pick a number from 1 to n. You have to guess which number I picked. Every time you guess wrong, I’ll tell you whether the number is higher or lower. You call a pre-defined API guess(int num) which returns 3 possible results (-1, 1, or 0): -1 : My number is lower 1 : My number is higher 0 : Congrats!

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below. For example, given the following triangle [ [2], [3,4], [6,5,7], [4,1,8,3] ] The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11). Note: Bonus point if you are able to do this using only O(n) extra space, where n is the total number of rows in the triangle.

Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm? Hint: Expected runtime complexity is in O(log n) and the input is sorted. Solution: public class Solution { public int hIndex(int[] citations) { int len = citations.length; int lo=0, hi=len-1; while(lo<=hi){ int mid = (lo+hi)/2; if(citations[mid]<len-mid) lo=mid+1; else if(citations[mid]>len-mid) hi=mid-1; else return len-mid; } return len-lo; } }

Given an array of citations (each citation is a non-negative integer) of a researcher, write a function to compute the researcher’s h-index. According to the definition of h-index on Wikipedia: “A scientist has index h if h of his/her N papers have at least h citations each, and the other N − h papers have no more than h citations each.” For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total and each of them had received 3, 0, 6, 1, 5 citations respectively.

Suppose we abstract our file system by a string in the following manner: The string “dir\n\tsubdir1\n\tsubdir2\n\t\tfile.ext” represents: dir subdir1 subdir2 file.ext The directory dir contains an empty sub-directory subdir1 and a sub-directory subdir2 containing a file file.ext. The string “dir\n\tsubdir1\n\t\tfile1.ext\n\t\tsubsubdir1\n\tsubdir2\n\t\tsubsubdir2\n\t\t\tfile2.ext” represents: dir subdir1 file1.ext subsubdir1 subdir2 subsubdir2 file2.ext The directory dir contains two sub-directories subdir1 and subdir2. subdir1 contains a file file1.ext and an empty second-level sub-directory subsubdir1. subdir2 contains a second-level sub-directory subsubdir2 containing a file file2.ext.

Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. For example, Given 1->4->3->2->5->2 and x = 3, return 1->2->2->4->3->5. Solution: /** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next;

Additive number is a string whose digits can form additive sequence. A valid additive sequence should contain at least three numbers. Except for the first two numbers, each subsequent number in the sequence must be the sum of the preceding two. For example: “112358” is an additive number because the digits can form an additive sequence: 1, 1, 2, 3, 5, 8. 1 + 1 = 2, 1 + 2 = 3, 2 + 3 = 5, 3 + 5 = 8 “199100199” is also an additive number, the additive sequence is: 1, 99, 100, 199.

Write a program to find the n-th ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the first 10 ugly numbers. Note that 1 is typically treated as an ugly number. Hint: The naive approach is to call isUgly for every number until you reach the nth one. Most numbers are not ugly.