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// Source : https://leetcode.com/problems/mini-parser/
// Author : Hao Chen
// Date : 2016-08-24
/***************************************************************************************
*
* 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
* class NestedInteger {
* public:
* // Constructor initializes an empty nested list.
* NestedInteger();
*
* // Constructor initializes a single integer.
* NestedInteger(int value);
*
* // Return true if this NestedInteger holds a single integer, rather than a nested list.
* bool isInteger() const;
*
* // Return the single integer that this NestedInteger holds, if it holds a single integer
* // The result is undefined if this NestedInteger holds a nested list
* int getInteger() const;
*
* // Set this NestedInteger to hold a single integer.
* void setInteger(int value);
*
* // Set this NestedInteger to hold a nested list and adds a nested integer to it.
* void add(const NestedInteger &ni);
*
* // Return the nested list that this NestedInteger holds, if it holds a nested list
* // The result is undefined if this NestedInteger holds a single integer
* const vector<NestedInteger> &getList() const;
* };
*/
class Solution {
public:
NestedInteger deserialize(string s) {
if (s.size()==0) return NestedInteger();
int pos = 0;
if (s[pos]!='[') return atoni(s, pos);
return helper(s, ++pos);
}
private:
NestedInteger helper(string& s, int& pos) {
NestedInteger ni;
while ( s[pos] != ']' && pos < s.size() ) {
if (s[pos]=='-' || isnum(s[pos])){
ni.add(atoni(s, pos));
}else if (s[pos] == '[') {
pos++;
ni.add(helper(s, pos));
}else {
pos++;
}
}
pos++;
return ni;
}
NestedInteger atoni(string& s, int& pos) {
int sign = 1;
int num = 0;
if (s[pos]=='-') {
sign = -1;
pos++;
}
for (; pos < s.size(); pos++) {
if (isnum(s[pos])) {
num = num * 10 + s[pos] - '0';
}else{
break;
}
}
return NestedInteger(sign * num);
}
bool isnum(char& c) {
return (c >='0' && c <='9');
}
};