leecode更新

Leecode/src/main/java/com/markilue/leecode/hot100/second/T46_105_BuildTree.java

@@ -0,0 +1,56 @@
+package com.markilue.leecode.hot100.second;
+
+import com.markilue.leecode.tree.TreeNode;
+
+/**
+ * @BelongsProject: Leecode
+ * @BelongsPackage: com.markilue.leecode.hot100.second
+ * @Author: marklue
+ * @CreateTime: 2023/4/16 11:15
+ * @Description: TODO  力扣105  根据前序遍历和中序遍历构造树
+ * @Version: 1.0
+ */
+public class T46_105_BuildTree {
+
+    int index = 0;
+
+    public TreeNode buildTree(int[] preorder, int[] inorder) {
+
+        return buildChild(preorder, inorder, 0, inorder.length - 1);
+
+    }
+
+    public TreeNode buildChild(int[] preorder, int[] inorder, int inStart, int inEnd) {
+        if (inStart > inEnd) {
+            return null;
+        }
+        TreeNode root = new TreeNode(preorder[index]);
+        index++;
+        int in = findIndex(inorder, inStart, inEnd, root.val);
+        root.left = buildChild(preorder, inorder, inStart, in - 1);
+        root.right = buildChild(preorder, inorder, in + 1, inEnd);
+        return root;
+
+    }
+
+    /**
+     * 在start和end的范围中寻找target
+     *
+     * @param inorder
+     * @param start
+     * @param end
+     * @param target
+     * @return
+     */
+    public int findIndex(int[] inorder, int start, int end, int target) {
+
+        while (start < end) {
+            if (inorder[start] == target) {
+                return start;
+            }
+            start++;
+        }
+        return -1;//没找到
+
+    }
+}