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What is time and space complexity to evaluate postfix expression ?

Algorithm

1. Read all the symbols from left to right of the postfix expression

2. If the reading symbol is  $operand$ then push into the stack

3. If the reading symbol is  $operator$, then perform two pop operations, do the arithmetic operation and again pushed the resultant into the stack

4. finally, perform a pop operation and print the popped value as the final result.

Time complexity of evaluation algorithm is $O(n)$ where n is the number of characters in input expression.

Can u explain how the time complexity is O(n) ?
there are n characters in input expression array and we  are scanning it from left to right, so the loop will run for n times

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