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VistasHow to fix issue in my "isParenthesisValid" algorithm code
I am solving an algorithm question whereby it requires me to ensure that brackets, parenthesis and braces are put in the correct order or sequence.
Here is a link to the question, https://leetcode.com/problems/valid-parentheses/
An example is shown below:
Here is my code for the solution:
const isParenthesisValid = (params) => {
myList = []
lastElement = myList[myList.length - 1]
for (let i = 0; i < params.length; i++) {
if (params[i] === "(" || params[i] === "[" || params[i] === "{" ) {
myList.push(params[i])
} else if ((params[i] === ")" && lastElement === "(") || (params[i] === "]" && lastElement === "[") || (params[i] === "}" && lastElement === "{")) {
myList.pop()
} else return false
}
return myList.length ? false : true
}
// I get false as an answer everytime whether the pattern is correct or wrong
// false
console.log(isParenthesisValid("[()]"))
But I don't know why I get false everytime, I have compared my answer with someones else answer who did the same thing but it seems I am omitting something not so obvious.
I hope someone can point out in my code where i am getting it wrong.
1 Respuestas
Responde la pregunta0
Your lastElement retrieves the last element of the list at the start of the program - when there is no such element - so it's always undefined. You need to retrieve the value inside the loop instead.
const isParenthesisValid = (params) => {
myList = []
for (let i = 0; i < params.length; i++) {
const lastElement = myList[myList.length - 1]
if (params[i] === "(" || params[i] === "[" || params[i] === "{" ) {
myList.push(params[i])
} else if ((params[i] === ")" && lastElement === "(") || (params[i] === "]" && lastElement === "[") || (params[i] === "}" && lastElement === "{")) {
myList.pop()
} else return false
}
return myList.length ? false : true
}
console.log(isParenthesisValid("[()]"))Or, a bit more readably:
const isParenthesisValid = (input) => {
const openDelimiters = [];
for (const delim of input) {
const lastElement = openDelimiters[openDelimiters.length - 1];
if (delim === "(" || delim === "[" || delim === "{") {
openDelimiters.push(delim)
} else if ((delim === ")" && lastElement === "(") || (delim === "]" && lastElement === "[") || (delim === "}" && lastElement === "{")) {
openDelimiters.pop()
} else return false
}
return openDelimiters.length === 0;
}
console.log(isParenthesisValid("[()]"))Another approach, linking each delimiter with an object:
const delims = {
')': '(',
'}': '{',
']': '[',
};
const isParenthesisValid = (input) => {
const openDelimiters = [];
for (const delim of input) {
if ('([{'.includes(delim)) {
openDelimiters.push(delim)
} else if (')]}'.includes(delim) && openDelimiters[openDelimiters.length - 1] === delims[delim]) {
openDelimiters.pop()
} else return false
}
return openDelimiters.length === 0;
}
console.log(isParenthesisValid("[()]"))