Question

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Stats

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Analysis

This is exactly the same question as “Construct Binary Tree from Preorder and Inorder”.

Solution

I post the code from this article.

Code

public TreeNode buildTree(int[] inorder, int[] postorder) {
    int inStart = 0, inEnd = inorder.length-1;
    int postStart =0, postEnd = postorder.length-1;
    return buildTree(inorder, inStart, inEnd, postorder, postStart, postEnd);
}

public TreeNode buildTree(int[] inorder, int inStart, int inEnd, 
                          int[] postorder, int postStart, int postEnd){
    if(inStart > inEnd || postStart > postEnd)
        return null;
    int rootValue = postorder[postEnd];
    TreeNode root = new TreeNode(rootValue);
    int k=0;
    for(int i=0; i< inorder.length; i++){
        if(inorder[i]==rootValue){
            k = i;
            break;
        }
    }
    root.left = buildTree(inorder, inStart, k-1, 
        postorder, postStart, postStart+k-(inStart+1));
    root.right = buildTree(inorder, k+1, inEnd, 
        postorder, postStart+k-inStart, postEnd-1);
    return root;
}