feat: Construct Binary Tree From Preorder And Inorder Traversal

 #253

Author: donghyeon95

construct-binary-tree-from-preorder-and-inorder-traversal/donghyeon95.java

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+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+
+/**
+ * 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 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 void setVal(int val) {
+		this.val = val;
+	}
+
+	public void setLeft(TreeNode left) {
+		this.left = left;
+	}
+
+	public void setRight(TreeNode right) {
+		this.right = right;
+	}
+
+	public int getVal() {
+		return val;
+	}
+
+	public TreeNode getLeft() {
+		return left;
+	}
+
+	public TreeNode getRight() {
+		return right;
+	}
+}
+
+class Solution {
+	int[] preList;
+	List<Integer> inList;
+	HashMap<Integer, TreeNode> treeNodes = new HashMap<>();
+
+	public TreeNode buildTree(int[] preorder, int[] inorder) {
+		preList = preorder;
+		inList = Arrays.asList(Arrays.stream(inorder).boxed().toArray(Integer[]::new));
+		List<Integer> preL = Arrays.asList(Arrays.stream(preorder).boxed().toArray(Integer[]::new));
+
+		int preIndex = 0;
+		int rootVal = preorder[0];
+		TreeNode root = new TreeNode(rootVal);
+		treeNodes.put(rootVal, root);
+
+		while (preIndex < preList.length - 1) {
+			System.out.println(preIndex);
+			int inIndex = inList.indexOf(preList[preIndex]);
+			int inNextIndex = inList.indexOf(preList[preIndex + 1]);
+
+			TreeNode node = new TreeNode(preList[preIndex + 1]);
+			treeNodes.put(preList[preIndex + 1], node);
+
+			if (inIndex > inNextIndex) {
+				// 현재 node의 왼쪽 자식으로
+				TreeNode nowNode = treeNodes.get(preList[preIndex]);
+				nowNode.setLeft(node);
+			} else {
+				// inorder의 앞 중에서 가장 처음 inList에서 앞인게
+				int value = 0;
+				int ii = inNextIndex;
+				while (ii >= 0) {
+					value = inorder[ii - 1];
+					int i = preL.indexOf(value);
+					if (i < preIndex + 1) {
+						treeNodes.get(preList[i]).setRight(node);
+						break;
+					}
+					ii--;
+				}
+
+			}
+
+			preIndex++;
+		}
+
+		return treeNodes.get(rootVal);
+	}
+
+}
+
+