Construct Tree From Inorder and Postorder in Java - Source Code

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

       return buildTree(inorder, inStart, inEnd, postorder, postStart, postEnd);
   }

   public TreeNode buildTree(char[] inorder, int inStart, int inEnd, 
                           char[] postorder, int postStart, int postEnd){
       if(inStart > inEnd || postStart > postEnd)
           return null;

       char rootValue = postorder[postEnd];
       //if(!isOperator(rootValue)) return null;
       TreeNode root = new TreeNode(rootValue);

       int k=0;
       for(int i=inStart; i< inorder.length; i++){
           if(inorder[i]==rootValue){
               //if(inorder[i]=='~') continue;
            k = i;
               break;
           }
       }
       

       root.left = buildTree(inorder, inStart, k-1, postorder, postStart, postStart+k-(inStart+1));
       // Becuase k is not the length, it it need to -(inStart+1) to get the length
       root.right = buildTree(inorder, k+1, inEnd, postorder, postStart+k-inStart, postEnd-1);
       // postStart+k-inStart = postStart+k-(inStart+1) +1
       return root;
   }
   
 }