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Add Solution2.java to problems 0105

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solution/0105.Construct Binary Tree from Preorder and Inorder Traversal
- Solution2.java

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	`1`	`+/**`
	`2`	`+ * Definition for a binary tree node.`
	`3`	`+ * public class TreeNode {`
	`4`	`+ * int val;`
	`5`	`+ * TreeNode left;`
	`6`	`+ * TreeNode right;`
	`7`	`+ * TreeNode(int x) { val = x; }`
	`8`	`+ * }`
	`9`	`+ */`
	`10`	`+class Solution {`
	`11`	`+`
	`12`	`+ private int idx;`
	`13`	`+ private int[] preorder;`
	`14`	`+ private Map<Integer, Integer> map = new HashMap<>();`
	`15`	`+`
	`16`	`+ public TreeNode buildTree(int[] preorder, int[] inorder) {`
	`17`	`+ this.idx = 0;`
	`18`	`+ this.preorder = preorder;`
	`19`	`+ int index = 0;`
	`20`	`+ for (int value : inorder) {`
	`21`	`+ map.put(value, index ++);`
	`22`	`+ }`
	`23`	`+ return buildTree(0, inorder.length);`
	`24`	`+ }`
	`25`	`+`
	`26`	`+ private TreeNode buildTree(int left, int right) {`
	`27`	`+ if (left >= right) return null;`
	`28`	`+ int rootVal = preorder[idx ++];`
	`29`	`+ int index = map.get(rootVal);`
	`30`	`+`
	`31`	`+ TreeNode root = new TreeNode(rootVal);`
	`32`	`+ root.left = buildTree(left, index);`
	`33`	`+ root.right = buildTree(index + 1, right);`
	`34`	`+ return root;`
	`35`	`+ }`
	`36`	`+}`

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