Merge pull request #103 from Joshua-Lu/patch-20

更新 0654.最大二叉树 Java版本

problems/0654.最大二叉树.md

@@ -224,27 +224,32 @@ root->right = traversal(nums, maxValueIndex + 1, right);
 
 
 Java：
-```java
+
+```Java
 class Solution {
     public TreeNode constructMaximumBinaryTree(int[] nums) {
-        if (nums.length == 0) return null;
-        return constructMaximumBinaryTree(nums,0,nums.length);
+        return constructMaximumBinaryTree1(nums, 0, nums.length);
     }
 
-    private TreeNode constructMaximumBinaryTree(int[] nums, int begin, int end) {
-        if (begin == end) return null;
-
-        int rootValue = nums[begin];
-        int index = begin;
-        for (int i = begin; i < end ; i++) {
-            if (nums[i] > rootValue) {
-                rootValue = nums[i];
-                index = i;
+    public TreeNode constructMaximumBinaryTree1(int[] nums, int leftIndex, int rightIndex) {
+        if (rightIndex - leftIndex < 1) {// 没有元素了
+            return null;
+        }
+        if (rightIndex - leftIndex == 1) {// 只有一个元素
+            return new TreeNode(nums[leftIndex]);
+        }
+        int maxIndex = leftIndex;// 最大值所在位置
+        int maxVal = nums[maxIndex];// 最大值
+        for (int i = leftIndex + 1; i < rightIndex; i++) {
+            if (nums[i] > maxVal){
+                maxVal = nums[i];
+                maxIndex = i;
             }
         }
-        TreeNode root = new TreeNode(rootValue);
-        root.left = constructMaximumBinaryTree(nums, begin,index);
-        root.right = constructMaximumBinaryTree(nums,index+1,end);
+        TreeNode root = new TreeNode(maxVal);
+        // 根据maxIndex划分左右子树
+        root.left = constructMaximumBinaryTree1(nums, leftIndex, maxIndex);
+        root.right = constructMaximumBinaryTree1(nums, maxIndex + 1, rightIndex);
         return root;
     }
 }