LeetCode in Kotlin

385. Mini Parser

Medium

Given a string s represents the serialization of a nested list, implement a parser to deserialize it and return the deserialized NestedInteger.

Each element is either an integer or a list whose elements may also be integers or other lists.

Example 1:

Input: s = “324”

Output: 324

Explanation: You should return a NestedInteger object which contains a single integer 324.

Example 2:

Input: s = “[123,[456,[789]]]”

Output: [123,[456,[789]]]

Explanation: Return a NestedInteger object containing a nested list with 2 elements:

1. An integer containing value 123.

2. A nested list containing two elements:

   i. An integer containing value 456.

   ii. A nested list with one element:

   a. An integer containing value 789

Constraints:

• 1 <= s.length <= 5 * 104
• s consists of digits, square brackets "[]", negative sign '-', and commas ','.
• s is the serialization of valid NestedInteger.
• All the values in the input are in the range [-106, 106].

Solution

import com_github_leetcode.NestedInteger

/*
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * class NestedInteger {
 *     // Constructor initializes an empty nested list.
 *     constructor()
 *
 *     // Constructor initializes a single integer.
 *     constructor(value: Int)
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     fun isInteger(): Boolean
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     fun getInteger(): Int?
 *
 *     // Set this NestedInteger to hold a single integer.
 *     fun setInteger(value: Int): Unit
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     fun add(ni: NestedInteger): Unit
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     fun getList(): List<NestedInteger>?
 * }
 */
class Solution {
    private var i = 0
    fun deserialize(s: String): NestedInteger {
        return getAns(s)
    }

    private fun getAns(s: String): NestedInteger {
        return if (s[i] == '[') {
            val ni = NestedInteger()
            i++
            while (i < s.length && s[i] != ']') {
                ni.add(getAns(s))
            }
            i++
            ni
        } else if (s[i] == ',') {
            i++
            getAns(s)
        } else {
            var x = 0
            var m = 1
            if (s[i] == '-') {
                i++
                m = -1
            }
            while (i < s.length && Character.isDigit(s[i])) {
                x = x * 10 + s[i++].code - '0'.code
            }
            x *= m
            NestedInteger(x)
        }
    }
}

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