654-最大二叉树

力扣654

https://leetcode-cn.com/problems/maximum-binary-tree/

当前节点任务：数组中找到最大的并构造节点，递归左右两边子数组构造出左右节点

由于默认函数没有必要的参数，所以得自己写一个，必要的参数如上面所说：左右子数组，所以需要start和end参数

public TreeNode constructMaximumBinaryTree(int[] nums) {
    return buildTree(nums, 0, nums.length - 1);
}

public TreeNode buildTree(int[] nums, int start, int end) {
    if (start > end) return null;
    int rootIdx = findMax(nums, start, end);
    TreeNode root = new TreeNode(nums[rootIdx]);
    root.left = buildTree(nums, start, rootIdx - 1);
    root.right = buildTree(nums, rootIdx + 1, end);
    return root;
}

public int findMax(int[] nums, int start, int end){
    int maxIdx = start;
    for (int i = start; i <= end; i++) {
        if (nums[i] > nums[maxIdx]){
            maxIdx = i;
        }
    }
    return maxIdx;
}