cangoal

//
public boolean search(int[] nums, int target) {
        if(nums == null || nums.length == 0) return false;
        int left = 0, right = nums.length - 1;
        while(left <= right){
            while(nums[left] == nums[right] && left < right){
                right--;
            }
            int mid = (left + right) / 2;
            if(nums[mid] == target) return true;

cangoal

//
public ListNode deleteDuplicates(ListNode head) {
        if(head == null) return head;
        ListNode pre = head, cur = head.next;
        while(cur != null){
            if(cur.val != pre.val){
                cur = cur.next;
                pre = pre.next;
            } else {
                pre.next = cur.next;

cangoal

//
public ListNode deleteDuplicates(ListNode head) {
        if(head == null) return head;
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        ListNode pre = dummyNode;
        while(head != null && head.next != null){
            if(head.val == head.next.val){
                while(head.next != null && head.val == head.next.val){
                    head = head.next;

cangoal

//
public ListNode partition(ListNode head, int x) {
        if(head == null) return head;
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        ListNode first = dummyNode, second = null;
        while(head != null){
            if(head.val >= x){
                if(second == null){
                    second = head;

cangoal

//
public List<Integer> grayCode(int n) {
        ArrayList<Integer> ret = new ArrayList<Integer>();
        if(n < 0) return ret;
        ret.add(0);
        if(n == 0) return ret;
        for(int i=0; i<n; i++){
            ArrayList<Integer> temp = new ArrayList<>();
            for(int j=ret.size()-1; j>=0; j--){
                temp.add((1<<i) + ret.get(j)); // the priority of +/- operation is higher then >>/<< shift operation

cangoal

//
    public ListNode newhead = null;
    public ListNode reverseList(ListNode head) {
        if(head == null) return head;
        helper(head, head.next);
        return newhead;
    }
    
    public void helper(ListNode pre, ListNode cur){
        if(cur == null){

cangoal

//
public ListNode reverseBetween(ListNode head, int m, int n) {
        if(head == null || m == n) return head;
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        ListNode walker = dummyNode, runner = dummyNode;
        int i=1;
        while(i < m){
            walker = walker.next;
            runner = runner.next;

cangoal

public ArrayList<ArrayList<String>> partition(String s) {
        ArrayList<ArrayList<String>> ret = new ArrayList<ArrayList<String>>();
        if(s == null || s.length()==0) return ret;
        helper(ret, s, new ArrayList<String>());
        return ret;
    }
    
    public void helper(ArrayList<ArrayList<String>> ret, String s, ArrayList<String> lst){
        if(s.length() == 0){
            ret.add(new ArrayList<String>(lst));

cangoal

//
public int canCompleteCircuit(int[] gas, int[] cost) {
        if(gas == null || gas.length == 0 || cost == null || cost.length == 0) return -1;
        int total = 0, local = 0, index = 0;
        for(int i=0; i<gas.length; i++){
            total += gas[i] - cost[i];
            local += gas[i] - cost[i];
            if(local < 0){
                index = i + 1; // don't write index = i;
                local = 0;

cangoal

//
public int candy(int[] ratings) {
        if(ratings == null || ratings.length == 0) return 0;
        int[] candy = new int[ratings.length];
        candy[0] = 1;
        for(int i=1; i<candy.length; i++){
            if(ratings[i] > ratings[i-1]){
                candy[i] = candy[i-1] + 1;
            } else {
                candy[i] = 1;