LeetCode.385 Mini Parser

题目：

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.

分析1（递归实现-推荐）：

/** * // 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(); * } */class Solution {    public NestedInteger deserialize(String s) {        //给定字符串，实现其特定返回类型        //思路：递归实现，对于属于同一层的直接添加，非同一层的递归将其中元素添加        NestedInteger nest=new NestedInteger();        //防止空串        if(s.length()==0||s==null) return nest;        if(s.charAt(0)!='['){            //防止只有数字的情况            nest.setInteger(Integer.parseInt(s));            return nest;        }                //空串[]        if(s.length()==2) {            return nest;        }                int start=1;        int layer=1;        for(int i=1;i<s.length();i++){            char ch=s.charAt(i);            if(layer==1&&(ch==','||i==s.length()-1)){                //递归实现其中的子集合                nest.add(deserialize(s.substring(start,i)));                start=i+1;            }            if(ch=='['){                //新的一层                layer++;            }else if(ch==']'){                layer--;            }        }        return nest;            }}

分析2（stack实现-易理解）：

/** * // 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(); * } */class Solution {    public NestedInteger deserialize(String s) {        //给定字符串，实现其特定返回类型        //思路：对整个字符串拆分需要判断当前是否是一个子集还是数字。同341使用stack                if(s.charAt(0)!='['){            //防止只有一个数字的情况            return new NestedInteger(Integer.valueOf(s));        }                //对字符串遍历        Stack<NestedInteger> stack=new Stack<NestedInteger>();        NestedInteger cur=null;        //用来表示标识对一个元素完成读取        int high=0;        for(int i=0;i<s.length();i++){            char ch=s.charAt(i);            if(ch=='['){                //当到下一个元素之前，判断前面一个元素是否满足(大的范围)                if(cur!=null){                    stack.push(cur);                }                cur=new NestedInteger();                high=i+1;            }else if(ch==']'){                //对字符串截断                String str=s.substring(high,i);                //判断该字符串                if(!str.isEmpty()){                    cur.add(new NestedInteger(Integer.valueOf(str)));                }                if(!stack.isEmpty()){                    //同一个范围的，在一个NestedInteger集合中                    NestedInteger pop=stack.pop();                    pop.add(cur);                    cur=pop;                }                high=i+1;            }else if(ch==','){                //判断是大范围的子集，还是小范围里面的子集                if(s.charAt(i-1)!=']'){                    //大范围                    String str=s.substring(high,i);                    //直接添加进行                    cur.add(new NestedInteger(Integer.valueOf(str)));                }                //重新修改游标                high=i+1;            }        }        return cur;    }}