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题目：Construct Binary Tree from Preorder and Inorder Traversal
<span style="font-size:18px;">/**LeetCode * 题意：给定一个二叉树的先序遍历和中序遍历的序列，重建二叉树* 思路：先序遍历的第一个节点是父节点，中序遍历从第一个节点到父节点的都是父节点的左子树，父节点后面的都是父节点的右子树* Definition for binary tree* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/
package javaTrain;public class Train20 {public TreeNode buildTree(int[] preorder, int[] inorder) {int n = preorder.length;if(n == 0) return null;int m = 0;int num = preorder[0];boolean tag = true;for(int i = 0;i < n;i++){ if(inorder[i] == num)break;m++;}int[] leftPre = new int[m];int[] leftIn = new int[m];int[] rightPre = new int[m-n-1];int[] rightIn = new int[m-n-1];for(int j = 0;j < n;j++){if(j == num-1) tag = false;if(tag){leftIn[j] = inorder[j];leftPre[j] = preorder[j+1];}else{rightIn[j-num-1] = inorder[j];rightPre[j] = preorder[j+1];}}TreeNode root = new TreeNode(num);root.left = buildTree(leftPre,leftIn);root.right = buildTree(rightPre,rightIn);return root;}
}
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