Stack • Applications

Redundant Brackets

Given a mathematical expression, determine if it contains any redundant brackets. `(a+b)` is useful, but `((a+b))` contains a redundant outer shell.

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The Definition

Brackets are only useful if they enclose an operator. For example `(a+b)` encloses `+`. `(a)` encloses no operators, making it mathematically useless (redundant).

The Stack Strategy

Push everything (open brackets, operators, operands) onto a stack EXCEPT closing brackets. When you see a closing bracket, start popping.

The Check

Pop until you hit the matching open bracket. If you didn't pop any operators (`+`, `-`, `*`, `/`) during that process, the brackets were redundant!

((a+b))

Analysis Stack

Empty

Code Tracker

:::

1function hasRedundant(exp) {

2 let stack = [];

3 for (let char of exp) {

4 if (char === ')' || char === '}' || char === ']') {

5 let isRedundant = true;

6 let top = stack.pop();

7 while (top !== '(' && top !== '{' && top !== '[') {

8 if (top === '+' || top === '-' || top === '*' || top === '/') {

9 isRedundant = false;

10 }

11 top = stack.pop();

12 }

13 if (isRedundant) return true;

14 } else {

15 stack.push(char);

16 }

17 }

18 return false;

19}