BiruLyu

public class Solution {
    public String convert(String s, int numRows) {
        //String res = "";
        if(s == null || s == "" || numRows == 1) return s;
        //String[] eachRow = new String[numRows];
        StringBuilder[] eachRow = new StringBuilder[numRows];
        for (int i = 0; i < eachRow.length; i++) eachRow[i] = new StringBuilder();// Initialization!!!!
        int direct = -1;
        int j = 0;
        for(int i = 0; i < s.length(); i++){

BiruLyu

   class Solution {
    public int myAtoi(String str) {
        if (str == null || str.length() < 1) return 0;
        int res = 0, i = 0, len = str.length(), sign = 1;
        while (str.charAt(i) == ' ') i++;
        if (str.charAt(i) == '-') {
            sign = -1;
            i++;
        } else if (str.charAt(i) == '+') {
            i++;

BiruLyu

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length < 1) return "";
        StringBuilder res = new StringBuilder();
        Arrays.sort(strs);
        char[] a = strs[0].toCharArray();
        char[] b = strs[strs.length - 1].toCharArray();
        for (int i = 0; i < a.length && i < b.length; i++) {
            if (a[i] == b[i]) {
                res.append(a[i]);

BiruLyu

class Solution {
    /**
     * Returns a index to the first occurrence of target in source,
     * or -1  if target is not part of source.
     * @param source string to be scanned.
     * @param target string containing the sequence of characters to match.
     */
    public int strStr(String source, String target) {
        if (source == null || target == null) {
            return -1;

BiruLyu

public class Solution {
    public String countAndSay(int n) {
        String baseStr = "1";
        List<String> res = new ArrayList<String>();
        res.add(baseStr);
        while(n > 1){
            int count = 1;
            StringBuilder temp = new StringBuilder();
            for(int i = 1; i < baseStr.length(); i++){
                if(baseStr.charAt(i) == baseStr.charAt(i - 1)){

BiruLyu

public class Solution {
    public boolean isPowerOfTwo(int n) {
        return (n > 0) && ( (n & (n - 1)) == 0);
    }
}

BiruLyu

class Solution {
public:
    bool isPowerOfThree(int n) {
        return fmod(log10(n)/log10(3), 1)==0;
    }
};

BiruLyu

public class Solution {
    public String multiply(String num1, String num2) {
        int len1 = num1.length();
        int len2 = num2.length();
        
        int[] res = new int[ len1 + len2];
        
        for(int i = len1 - 1; i >= 0; i-- ){
            for(int j = len2 - 1; j >=0; j-- ){
                int temp = (num1.charAt(i) - '0') * (num2.charAt(j) - '0') + res[i + j + 1];

BiruLyu

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {

BiruLyu

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {