力扣-105.从前序与中序遍历序列构造二叉树

题目链接

105.从前序与中序遍历序列构造二叉树

class Solution {
    public TreeNode buildTree(int[] preorder, int[] inorder) {
        if (preorder.length == 0)
            return null;
        TreeNode root = new TreeNode(preorder[0]);
        int index = 0;
        for (int i = 0; i < inorder.length; i++) {
            if (inorder[i] == preorder[0]) {
                index = i;
                break;
            }
        }
        int[] leftin = Arrays.copyOfRange(inorder, 0, index);
        int[] rightin = Arrays.copyOfRange(inorder, index + 1, inorder.length);
        int[] leftpre = Arrays.copyOfRange(preorder, 1, 1 + index);
        int[] rightpre = Arrays.copyOfRange(preorder, 1 + index, preorder.length);
        root.left = buildTree(leftpre, leftin);
        root.right = buildTree(rightpre, rightin);
        return root;
    }
}

小结：要熟悉java的API，拆分数组用Arrays.copyOfRange()，注意递归的写法即可。