雯雯熊孩子

罗马转数字，如果i位比i+1位小，那么说明是i+1位的字母代表数字 - i位的数字。例如： XL, X ( = 10) < L ( =50),那么应该为L-X = 40. 如果是这个情况，光标左移动两位。否则移动一位。 数字转字母，根据当前数字%dividor的情况，分为9, 5-8, 4, 1-3几种情况。 public class Solution {     public int rom

Given a range [m, n] where 0 For example, given the range [5, 7], you should return 4. 核心就是求m 和n的最高位是否在一个位置上。我们把n的所有低位置零，只剩下最高位，然后&m。结果或者是两个的最高位，或者是0. public int rangeBitwiseAnd(int m, i

Having an input stream of n, select k elements with equal probability. Algorithm:  1. select k elements into the result first 0....k-1 2. for k....n-1 elements, each time i, generate a random n

Count the number of k's between 0 and n. k can be 0 - 9. Example if n=12, in [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], we have FIVE 1's (1, 10, 11, 12) see: http://www.hawstein.com/post

EPI: https://code.google.com/p/elements-of-programming-interviews/source/browse/trunk/Square_root.cpp public static double sqrt(double num) { double left = 0, right = 0; if (num <

注意dividend, divisor 为边界的情况。还有j public int divide(int dividend, int divisor) { if (divisor == 0) { return Integer.MAX_VALUE; } int result = 0; if (d

Determine whether an integer is a palindrome. Do this without extra space. click to show spoilers. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of convertin

Given two numbers represented as strings, return multiplication of the numbers as a string. Note: The numbers can be arbitrarily large and are non-negative. public String multiply(String n

public class Solution {     public int atoi(String str) {         int sign = 1;         boolean checkSign = true;         boolean checkFirst = true;         int result = 0;                  for (int i

Given two integers representing the numerator and denominator of a fraction, return the fraction in string format. If the fractional part is repeating, enclose the repeating part in parentheses.

public int sqrt(int x) { if (x < 0) { return -1; } if (x == 0 || x == 1) { return x; } int high = x; int low = 1; while (low <= high) {

In data structure Hash, hash function is used to convert a string(or any other type) into an integer smaller than hash size and bigger or equal to zero. The objective of designing a hash function is t

注意n为负数的情况 public double pow(double x, int n) { int sign = n < 0 ? -1 : 1; n = Math.abs(n); double result = helper(x, n); return sign == 1 ? result : (double) 1/res

Given two binary strings, return their sum (also a binary string). For example, a = "11" b = "1" Return "100". 容易错的地方： public String addBinary(String a, String b) { String

Given an array of integers, every element appears three times except for one. Find that single one. Note: Your algorithm should have a linear runtime complexity. Could you implement it without u

public String getPermutation(int n, int k) { List num = new ArrayList(); for (int i = 0; i < n; i++) { num.add(i+1); } int factorial = 1; for (int i

public static List findPrime(int n) { List preResult = new ArrayList(); List result = new ArrayList(); for (int i = 1; i <= n; i++) { preResult.add(i); } int divisorInd = 1; // start fro

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA. Wri