cangoal

//
public int majorityElement(int[] nums) {
        if(nums == null || nums.length == 0) return -1;
        int ret = nums[0], count=1;
        for(int i=1; i<nums.length; i++){
            if(count == 0){
                ret = nums[i];
                count = 1;
            }
            else if(ret == nums[i]){

cangoal

//
public int trailingZeroes(int n) {
    int ret = 0;
    while(n != 0){
        ret += n/5;
        n = n/5;
    }
    return ret;
}
//

cangoal

//
public String largestNumber(int[] nums) {
        if(nums == null || nums.length==0) return null;
        String str = "";
        ArrayList<Integer> list = new ArrayList<>();
        for(int num : nums){
            list.add(num);
        }
        Collections.sort(list, comparator);
        for(int i=0; i<list.size(); i++){

cangoal

// better solution
public int reverseBits(int n) {
        int ret = 0;
        for(int i=0; i<32; i++){
            ret = (ret << 1) + (n & 1);
            n >>=1;
        }
        return ret;
    }

cangoal

public int hammingWeight(int n) {
        int ret = 0;
        while(n != 0){
            n &= n-1;
            ret++;
        }
        return ret;
    }

cangoal

//
public List<Integer> rightSideView(TreeNode root) {
        List<Integer> ret = new ArrayList<Integer>();
        helper(ret, root, 0);
        return ret;
    }
    
    private void helper(List<Integer> ret, TreeNode root, int level){
        if(root == null) return;
        if(ret.isEmpty() || level >= ret.size()){

cangoal

// BFS ---> note: this my cause issue when you encode the coordinates
public int numIslands(char[][] grid) {
        if(grid==null || grid.length==0) return 0;
        int count = 0;
        for(int i=0; i<grid.length; i++){
            for(int j=0; j<grid[0].length; j++){
                if(grid[i][j] == '1'){
                    count++;
                    setZeros(grid, i, j);
                }

cangoal

//
public int rangeBitwiseAnd(int m, int n) {
        while(m<n) n = n & (n-1);
        return n;
    }

//
 public int rangeBitwiseAnd(int m, int n) {
        return (n > m) ? (rangeBitwiseAnd(m/2, n/2) << 1) : m;
    }

cangoal

// O(1) space complexity
int digitSquareSum(int n) {
    int sum = 0, tmp;
    while (n) {
        tmp = n % 10;
        sum += tmp * tmp;
        n /= 10;
    }
    return sum;
}

cangoal

public ListNode removeElements(ListNode head, int val) {
        if(head == null) return head;
        ListNode dummyNode = new ListNode(0);
        dummyNode.next = head;
        ListNode pre = dummyNode;
        
        while(pre.next != null){
            ListNode cur = pre.next;
            if(cur.val == val){
                pre.next = pre.next.next;