private TreeNode gT(int[] preOrder, int pStart, int pEnd, int[] inOrder, int inStart, int inEnd){
        if(preOrder==null || inOrder==null || preOrder.length==0 || inOrder.length==0 || inStart>inEnd || pStart>pEnd){
            return null;
        }
        int childRootVal = preOrder[pStart];
        TreeNode childRoot = new TreeNode(childRootVal);
        int childRootInOrderIndex = -1;
        for(int i=inStart; i<=inEnd; i++){
            if(inOrder[i]==childRootVal){
                childRootInOrderIndex=i;
                break;
            }
        }
        if(childRootInOrderIndex==-1){
            return null;
        }
        int duration = childRootInOrderIndex-inStart;
        childRoot.left=gT(preOrder, pStart+1, pStart+duration, inOrder, inStart, childRootInOrderIndex-1);
        childRoot.right=gT(preOrder, pStart+duration+1,pEnd, inOrder, childRootInOrderIndex+1, inEnd);
        return childRoot;
    }