20. Valid Parentheses

Given a string of the brackets ()[]{}, return true if every bracket is closed by the same type in the correct order.

Push each opening bracket. A closing bracket must match the top of the stack. At the end, the stack must be empty.

1function isValid(s: string): boolean {
2  const pairs: Record<string, string> = { ")": "(", "]": "[", "}": "{" };
3  const stack: string[] = [];
4  for (const ch of s) {
5    if (!(ch in pairs)) stack.push(ch);
6    else if (stack.pop() !== pairs[ch]) return false;
7  }
8  return stack.length === 0;
9}

s

{

[

(

)

]

}

(

)

stack (bottom → top)

empty

Empty stack.

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