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Solution.java
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Solution.java
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package g0101_0200.s0105_construct_binary_tree_from_preorder_and_inorder_traversal;
// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Array #Hash_Table #Tree #Binary_Tree
// #Divide_and_Conquer #Data_Structure_II_Day_15_Tree #Big_O_Time_O(N)_Space_O(N)
// #2022_06_22_Time_3_ms_(86.35%)_Space_45.2_MB_(14.09%)
import com_github_leetcode.TreeNode;
import java.util.HashMap;
import java.util.Map;
/*
* 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;
* }
* }
*/
public class Solution {
private int j;
private Map<Integer, Integer> map = new HashMap<>();
public int get(int key) {
return map.get(key);
}
private TreeNode answer(int[] preorder, int[] inorder, int start, int end) {
if (start > end || j > preorder.length) {
return null;
}
int value = preorder[j++];
int index = get(value);
TreeNode node = new TreeNode(value);
node.left = answer(preorder, inorder, start, index - 1);
node.right = answer(preorder, inorder, index + 1, end);
return node;
}
public TreeNode buildTree(int[] preorder, int[] inorder) {
j = 0;
for (int i = 0; i < preorder.length; i++) {
map.put(inorder[i], i);
}
return answer(preorder, inorder, 0, preorder.length - 1);
}
}