qren0neu

class Solution {

    private int getVal(char c) {
        switch (c) {
            case 'I':
                return 1;
            case 'V':
                return 5;
            case 'X':
                return 10;

qren0neu

class Solution {
    public String longestCommonPrefix(String[] strs) {
        StringBuilder prefix = new StringBuilder();
        for (int i = 0; i < strs[0].length(); i++) {
            prefix.append(strs[0].charAt(i));
            for (int j = 1; j < strs.length; j++) {
                if (i >= strs[j].length() || prefix.charAt(i) != strs[j].charAt(i)) {
                    prefix.deleteCharAt(i);
                    return prefix.toString();   
                }

qren0neu

class Solution {
    public int lengthOfLastWord(String s) {
        s = s.trim(); // 1. trim
        char[] arr = s.toCharArray();
        int slow = 0;
        int fast = 0;
        while (fast < arr.length) {
            slow = fast;
            // skip the words
            while (fast < arr.length && arr[fast] != ' ') {

qren0neu

class Solution {
    public String reverseWords(String s) {
        s = s.trim();
        String[] spl = s.split(" ");
        StringBuilder sb = new StringBuilder();
        for (int i = spl.length - 1; i >= 0; i--) {
            if (!spl[i].trim().isEmpty()) {
                sb.append(spl[i]);
                if (i != 0) {
                    sb.append(" ");

qren0neu

class Solution {
    public List<List<Integer>> combine(int n, int k) {
        // 1 - n, contains
        List<List<Integer>> result = new LinkedList<>();
        List<Integer> current = new LinkedList<>();
        dfs(result, current, 1, n, k);
        return result;
    }

    private void dfs(List<List<Integer>> result, List<Integer> current,  int start, int n, int k) {

qren0neu

private char transform(char c) {
        if (c >= 'A' && c <= 'Z') {
            return (char)(c + 32);
        } else if (c >= 'a' && c <= 'z'  || c >= '0' && c <= '9') {
            return c;
        } else {
            return '!';
        }
    }

qren0neu

class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        // note: cost is from ith station to i+1 th station
        // find the point that gas is at the lowest, start from there
        int minGas = 0;
        int startPoint = 0;
        int currentGas = 0;
        for (int i = 0; i < gas.length; i++) {
            currentGas += (gas[i] - cost[i]);
            if (currentGas < minGas) {

qren0neu

class RandomizedSet {

    private int pos = 0;
    private Map<Integer, Integer> set = new HashMap<>();
    private int[] vals = new int[200001];

    public RandomizedSet() {
        
    }
    

qren0neu

class Solution {

    private void reverse(int[] arr) {
        int start = 0;
        int end = arr.length - 1;
        while (start < end) {
            int temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;

qren0neu

class Solution {
    public int jump(int[] nums) {
        // min steps of position n
        int[] dp = new int[nums.length];
        dp[0] = 0;
        for (int i = 0; i < nums.length; i++) {
            int reachableDistance = nums[i];
            for (int j = i + 1; j <= Math.min(nums.length - 1, i + reachableDistance); j++) {
                if (dp[j] == 0) {
                    dp[j] = dp[i] + 1;