Java日记2018-06-22

27. 二叉树的镜像

public void Mirror(TreeNode root) {
    if (root == null)
        return;
    swap(root);
    Mirror(root.left);
    Mirror(root.right);
}

private void swap(TreeNode root) {
    TreeNode t = root.left;
    root.left = root.right;
    root.right = t;
}

28 对称的二叉树

boolean isSymmetrical(TreeNode pRoot) {
    if (pRoot == null)
        return true;
    return isSymmetrical(pRoot.left, pRoot.right);
}

boolean isSymmetrical(TreeNode t1, TreeNode t2) {
    if (t1 == null && t2 == null)
        return true;
    if (t1 == null || t2 == null)
        return false;
    if (t1.val != t2.val)
        return false;
    return isSymmetrical(t1.left, t2.right) && isSymmetrical(t1.right, t2.left);
}

31. 栈的压入、弹出序列

public boolean IsPopOrder(int[] pushA, int[] popA) {
    int n = pushA.length;
    Stack<Integer> stack = new Stack<>();
    for (int pushIndex = 0, popIndex = 0; pushIndex < n; pushIndex++) {
        stack.push(pushA[pushIndex]);
        while (popIndex < n && stack.peek() == popA[popIndex]) {
            stack.pop();
            popIndex++;
        }
    }
    return stack.isEmpty();
}