385. Mini Parser**

最新推荐文章于 2019-12-10 17:10:56 发布

原创最新推荐文章于 2019-12-10 17:10:56 发布 · 324 阅读

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本文介绍了一种解析嵌套整数列表的算法，通过递归地处理输入字符串，将它转换为嵌套的整数对象。该解析器能处理单个整数及包含多个层级的列表。

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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.

/**
 * // 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.isEmpty())
        return null;
    if (s.charAt(0) != '[') // ERROR: special case
        return new NestedInteger(Integer.valueOf(s));
        
    Stack<NestedInteger> stack = new Stack<>();
    NestedInteger curr = null;
    int l = 0; // l shall point to the start of a number substring; 
               // r shall point to the end+1 of a number substring
    for (int r = 0; r < s.length(); r++) {
        char ch = s.charAt(r);
        if (ch == '[') {
            if (curr != null) {
                stack.push(curr);
            }
            curr = new NestedInteger();
            l = r+1;
        } else if (ch == ']') {
            String num = s.substring(l, r);
            if (!num.isEmpty())
                curr.add(new NestedInteger(Integer.valueOf(num)));
            if (!stack.isEmpty()) {
                NestedInteger pop = stack.pop();
                pop.add(curr);
                curr = pop;
            }
            l = r+1;
        } else if (ch == ',') {
            if (s.charAt(r-1) != ']') {
                String num = s.substring(l, r);
                curr.add(new NestedInteger(Integer.valueOf(num)));
            }
            l = r+1;
        }
    }
    
    return curr;
  }
}

总结：弄清楚。