day23打卡

28. 修剪二叉搜索树

1. 递归法

var trimBST = function (root,low,high) {
    if(root === null) {
        return null;
    }
    if(root.val < low) {
        let right = trimBST(root.right, low, high);
        return right;
    }
    if(root.val > high) {
        let left = trimBST(root.left, low, high);
        return left;
    }
    root.left = trimBST(root.left, low, high);
    root.right = trimBST(root.right, low, high);
    return root;
 }

2. 迭代法

29. 将有序数组转换为二叉搜索树

1. 递归法

var sortedArrayToBST = function (nums) {
    const buildTree = (Arr, left, right) => {
        if (left > right)
            return null;

        let mid = Math.floor(left + (right - left) / 2);

        let root = new TreeNode(Arr[mid]);
        root.left = buildTree(Arr, left, mid - 1);
        root.right = buildTree(Arr, mid + 1, right);
        return root;
    }
    return buildTree(nums, 0, nums.length - 1);
};

30. 把二叉搜索树转换为累加树

1. 递归法

var convertBST = function(root) {
    let pre = 0;
    const ReverseInOrder = (cur) => {
        if(cur) {
            ReverseInOrder(cur.right);
            cur.val += pre;
            pre = cur.val;
            ReverseInOrder(cur.left);
        }
    }
    ReverseInOrder(root);
    return root;
};

31. 总结篇