[LeetCode] 385. Mini Parser

Given a nested list of integers represented as a string, implement a parser to deserialize it.
Each element is either an integer, or a list -- whose elements may also be integers or other lists.
Note: You may assume that the string is well-formed:
  • String is non-empty.
  • String does not contain white spaces.
  • String contains only digits 0-9, [, - ,, ].
Example 1:
Given s = "324",

You should return a NestedInteger object which contains a single integer 324.
Example 2:
Given s = "[123,[456,[789]]]",

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.

Thought process:
Iterate through the string. There are five cases:
  1. Digit: keep track of current number.
  2. [: push the current NestedInteger onto stack and create a new NestedInteger.
  3. -: set sign to -1.
  4. ,: if the previous character is a digit, add the number into current NestedInteger. If the previous character is ], add the current NestedInteger to previous NestedInteger.
  5. ]: current NestedInteger is finished. Pop the NestedInteger from top of the stack.

Solution:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
/**
 * // This is the interface that allows for creating nested lists.
 * // You should not implement it, or speculate about its implementation
 * public interface NestedInteger {
 *     // Constructor initializes an empty nested list.
 *     public NestedInteger();
 *
 *     // Constructor initializes a single integer.
 *     public NestedInteger(int value);
 *
 *     // @return true if this NestedInteger holds a single integer, rather than a nested list.
 *     public boolean isInteger();
 *
 *     // @return the single integer that this NestedInteger holds, if it holds a single integer
 *     // Return null if this NestedInteger holds a nested list
 *     public Integer getInteger();
 *
 *     // Set this NestedInteger to hold a single integer.
 *     public void setInteger(int value);
 *
 *     // Set this NestedInteger to hold a nested list and adds a nested integer to it.
 *     public void add(NestedInteger ni);
 *
 *     // @return the nested list that this NestedInteger holds, if it holds a nested list
 *     // Return null if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
public class Solution {
    public NestedInteger deserialize(String s) {
        if (s.length() == 0) {
            return new NestedInteger();
        }
        if (s.charAt(0) != '[') {
            return new NestedInteger(Integer.parseInt(s));
        }
        NestedInteger current = null;
        Stack<NestedInteger> stack = new Stack<>();
        int left = 0;
        int right = 0;
        
        for (; right < s.length(); right++) {
            char c = s.charAt(right);
            if (c == '[') {
                if (current != null) {
                    stack.push(current);
                }
                current = new NestedInteger();
                left = right + 1;
            } else if (c == ']') {
                String number = s.substring(left, right);
                if (number.length() > 0) {
                    current.add(new NestedInteger(Integer.parseInt(number)));
                }
                if (!stack.isEmpty()) {
                    NestedInteger parent = stack.pop();
                    parent.add(current);
                    current = parent;
                }
                left = right + 1;
            } else if (c == ',') {
                if (s.charAt(right - 1) != ']') {
                    current.add(new NestedInteger(Integer.parseInt(s.substring(left, right))));
                }
                left = right + 1;
            }
        }
        
        return current;
    }
}

Time complexity: O(n).
Location: San Jose, CA, USA

Comments

Post a Comment

Popular posts from this blog

[LeetCode] 631. Design Excel Sum Formula

Your task is to design the basic function of Excel and implement the function of sum formula. Specifically, you need to implement the following functions: Excel(int H, char W):  This is the constructor. The inputs represents the height and width of the Excel form.  H  is a positive integer, range from 1 to 26. It represents the height.  W  is a character range from 'A' to 'Z'. It represents that the width is the number of characters from 'A' to  W . The Excel form content is represented by a height * width 2D integer array  C , it should be initialized to zero. You should assume that the first row of  C  starts from 1, and the first column of  C  starts from 'A'. void Set(int row, char column, int val):  Change the value at  C(row, column)  to be val. int Get(int row, char column):  Return the value at  C(row, column) . int Sum(int row, char column, List of Strings : numbers):  This function calculate and set the value at  C(row, column) , wh
Read more

[LeetCode] 269. Alien Dictionary

There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of  non-empty  words from the dictionary, where  words are sorted lexicographically by the rules of this new language . Derive the order of letters in this language. Example 1: Given the following words in dictionary, [ "wrt", "wrf", "er", "ett", "rftt" ] The correct order is:  "wertf" . Example 2: Given the following words in dictionary, [ "z", "x" ] The correct order is:  "zx" . Example 3: Given the following words in dictionary, [ "z", "x", "z" ] The order is invalid, so return  "" . Note: You may assume all letters are in lowercase. You may assume that if a is a prefix of b, then a must appear before b in the given dictionary. If the order is invalid, return an empty string
Read more

[LeetCode] 714. Best Time to Buy and Sell Stock with Transaction Fee

Your are given an array of integers  prices , for which the  i -th element is the price of a given stock on day  i ; and a non-negative integer  fee  representing a transaction fee. You may complete as many transactions as you like, but you need to pay the transaction fee for each transaction. You may not buy more than 1 share of a stock at a time (ie. you must sell the stock share before you buy again.) Return the maximum profit you can make. Example 1: Input: prices = [1, 3, 2, 8, 4, 9], fee = 2 Output: 8 Explanation: The maximum profit can be achieved by: Buying at prices[0] = 1 Selling at prices[3] = 8 Buying at prices[4] = 4 Selling at prices[5] = 9 The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8. Note: 0 < prices.length <= 50000 . 0 < prices[i] < 50000 . 0 <= fee < 50000 . Thought process: Each day there are two options, buy or sell. Use two variables buy and sell to keep track of the max profit. Solution: 1 2 3 4 5 6
Read more