Implement peek and write some test code to ensure that it's working.
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Implement peek and write some test code to ensure that it's working.
The peek method returns the topmost node's value or null if the stack is empty.
// some code above
peek() {
return this.top ? this.top.val : null;
}
In our solution, we use a ternary operator. If the top element exists, this.top.val will be returned; otherwise, null. We could rewrite it with an if statement as well:
// some code above
peek() {
if (this.top) {
return this.top.val;
}
return null;
}
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