Question

State the pseudo code and worst case running time to evaluate a prefix evaluation using a stack data structureState the pseudo code and worst case running time to evaluate a prefix evaluation using a stack data structure

Answer 1

Algorithm to evaluate prefix-expression

Step 1: start traversing expression from right to left
Step 2: If character at current position is an operand push it to Stack
Step 3: If the character at current position is an operator pop two operands from the Stack. Operate on these operands
according to the operator, and push the result to the Stack

Step 4: goto step-2 if complete expression is not traversed(or we reached at left end of expression).

finally,print value at the top of stack will give result of expression.

since we scan the expression once(right to left) and perform O(N) push(take O(1) time) and pop operations (take O(1) time)in worst case .

Therefore overall complexity = O(N)