iwilbert

    public static void drawHorizontalLine(byte[] screen, int width, int x1, int x2, int y) {
        int height = screen.length / width;
        if (y < 0 || y >= height || x1 < 0 || x1 >= screen.length * 8 || x2 < 0 || x2 >= screen.length * 8)
            return;
        int base = y * width / 8;
        int start = base + x1 / 8;
        int end = base + x2 / 8;
        
        byte mask1;
        if (x1 % 8 == 0)

iwilbert

    public int swapBits(int num) {
        return (num & 0x55555555) << 1 | (num & 0xAAAAAAAA) >> 1;
    }

iwilbert

    public int bitNumber(int a, int b) {
        int n = a ^ b;
        int cnt = 0;
        while (n > 0) {
            if ((n & 1) == 1)
                cnt++;
            n >>= 1;
        }
        return cnt;
    }

iwilbert

    public static String toBinary(double num) {
        if (num >= 1 || num < 0) {
            return "ERROR";
        }
        StringBuffer sb = new StringBuffer();
        sb.append("0.");
        int i;
        for (i = 0; i < 32 && num != 0; i++) {
            if (num >= 0.5) {
                sb.append(1);

iwilbert

    public static int insertMtoN(int N, int M, int i, int j) {
        int mask = (~(1 << (j - i + 1) - 1)) << i;
        return (N & mask) | (M << i);
    }

iwilbert

    public void allPaths(TreeNode root, int target) {
        if (root == null)
            return;
        int dep = depth(root);
        int[] path = new int[dep];
        findPaths(root, target, 0, path);
    }
    
    private void findPaths(TreeNode root, int target, int level, int[] path) {
        if (root == null)

iwilbert

    public boolean isSubtree(TreeNode t1, TreeNode t2) {
        if (t2 == null)
            return true;
        if (t1 == null)
            return false;
        if (isMatch(t1, t2))
            return true;
        return isSubtree(t1.left, t2) || isSubtree(t1.right, t2);
    }
    

iwilbert

    public TreeNode LCA(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null)
            return null;
        if (!isExisted(root, p) || !isExisted(root, q))
            return null;
        return LCA_helper(root, p, q);
    }
    
    private boolean isExisted(TreeNode root, TreeNode node) {
        if (root == null)

iwilbert

    public TreeNode getNext(TreeNode node) {
        if (node.right != null)
            return getMin(node.right);
        TreeNode parent = node.parent;
        while (parent != null && parent.right == node) {
            node = parent;
            parent = node.parent;
        }
        return parent;
    }

iwilbert

    public boolean isBST(TreeNode root) {
        return isBST_helper(root, Integer.MIN_VALUE, Integer.MAX_VALUE);
    }
    
    private boolean isBST_helper(TreeNode root, int minValue, int maxValue) {
        if (root == null)
            return true;
        return root.val > minValue && root.val < maxValue
                && isBST_helper(root.left, minValue, root.val)
                && isBST_helper(root.right, root.val, maxValue);