https://leetcode.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/
待优化:可以用 map 存一下每一个前序遍历元素对应的下标,这样更快一些。
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */
class Solution {
public TreeNode buildTree(int[] inorder, int[] postorder) {
return process(inorder, postorder, 0, inorder.length - 1, 0, postorder.length - 1);
}
public TreeNode process(int[] inorder, int[] postorder, int L1, int R1, int L2, int R2) {
if (L1 > R1) return null;
TreeNode root = new TreeNode(postorder[R2]);
for (int M1 = L1, n = 0; M1 <= R1; M1++, n++) {
if (inorder[M1] == postorder[R2]) {
root.left = process(inorder, postorder, L1, M1 - 1, L2, L2 + n - 1);
root.right = process(inorder, postorder, M1 + 1, R1, L2 + n, R2 - 1);
return root;
}
}
return root;
}
}
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