由前序遍历和中序遍历的到二叉树
题目:牛客网
/**
* Definition for binary tree
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution {
public static TreeNode buildTree(int[] preorder, int[] inorder) {
if(inorder.length==0 || preorder.length == 0)
return null;
return solve(preorder , 0, preorder.length-1, inorder, 0, inorder.length-1 );
}
public static TreeNode solve(int[] preorder,int pre_start, int pre_end, int[] inorder, int in_start, int in_end) {
if(in_start>in_end||pre_start>pre_end)
return null;
TreeNode root = new TreeNode(preorder[pre_start]);
int index=0;
for(int i=0;i<=in_end;i++){
if(inorder[i]==preorder[pre_start]){
index=i;
}
}
root.left = solve(preorder , pre_start+1, pre_start+index-in_start, inorder, in_start, index-1 );
root.right = solve(preorder , pre_start+index-in_start+1, pre_end , inorder, index+1, in_end);
return root;
}
}