LeetCode

100. 相同树

/**
 * 100. 相同的树
 */
public class IsSameTree {

    public boolean isSameTree(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }
        if (p != null && q != null && p.val == q.val) {
            return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
        }
        return false;
    }

    class TreeNode {
        int val;
        private TreeNode left;
        private TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }
}

101. 对称二叉树

/**
 * 101. 对称二叉树
 * 给定一个二叉树，检查它是否是镜像对称的。
 */
public class IsSymmetric {

    public boolean isSymmetric(TreeNode root) {
        return isMirror(root, root);
    }

    private boolean isMirror(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        }
        if (p == null || q == null) {
            return false;
        }
        return p.val == q.val && isMirror(p.left, q.right) && isMirror(p.right, q.left);
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }
}

104. 二叉树的最大深度

/**
 * 104. 二叉树的最大深度
 */
public class MaxDepth {

    public int maxDepth(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftDepth = maxDepth(root.left);
        int rightDepth = maxDepth(root.right);
        return Math.max(leftDepth, rightDepth) + 1;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }
}

108. 将有序数组转化成二叉搜索树

/**
 * 108. 将有序数组转换为二叉搜索树
 */
public class SortedArrayToBST {

    public TreeNode sortedArrayToBST(int[] nums) {
        if (nums == null || nums.length == 0) {
            return null;
        }
        return this.buildTree(nums, 0, nums.length-1);
    }

    private TreeNode buildTree(int[] nums, int l, int r) {
        if (l > r) {
            return null;
        }
        if (l == r) {
            return new TreeNode(nums[l]);
        }
       int mid = (l + r)/2;
       TreeNode root = new TreeNode(nums[mid]);
       root.left = buildTree(nums, 0, mid -1);
       root.right = buildTree(nums, mid + 1, r);
       return root;
    }

    class TreeNode {
        int val;
        TreeNode left;
        TreeNode right;
        TreeNode(int val) {
            this.val = val;
        }
    }
}

111. 二叉树最小深度