Let us consider an expression tree $($see example below$)$

Select one or more:a$.$ Printing the expression tree in postfix notation costs $\backslash (\backslash$mathrm$\{$O$\}\backslash$left$(2^\{$N$\}\backslash$right$)\backslash )$ where N is the number of nodesb. Building an expression tree from an expression in infix costs $\backslash ($ O$\backslash$left$($N$^\{2\}\backslash$right$)\backslash )$ where $\backslash ($ N $\backslash )$ is the number of elementsc. The expression tree only represents expressions in infix notationd. Leaf nodes can be operands or operatorse. Checking if $2$ expression trees are equal can be performed in $\backslash ($ O$($N$)\backslash )$ where $\backslash ($ N $\backslash )$ is the number of nodes