Question Definition
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.
Java Solution
public NestedInteger deserialize(String s) {
if(s.indexOf("[") < 0) return new NestedInteger(Integer.parseInt(s));
Deque<NestedInteger> deque = new ArrayDeque<>();
NestedInteger cur = null;
int num = 0;
boolean positive = false;
for(int i = 0; i < s.length(); i++){
char c = s.charAt(i);
if(c == '['){
if(cur != null)
deque.push(cur);
cur = new NestedInteger();
} else if(c == ']'){
if(s.charAt(i - 1) >= '0' && s.charAt(i - 1) <= '9'){
if(positive)
num = -num;
cur.add(new NestedInteger(num));
}
NestedInteger parent = deque.poll();
if(parent == null)
return cur;
parent.add(cur);
cur = parent;
num = 0;
positive = false;
} else if(c == ','){
if(s.charAt(i - 1) >= '0' && s.charAt(i - 1) <= '9'){
if(positive)
num = -num;
cur.add(new NestedInteger(num));
}
num = 0;
positive = false;
} else {
if(c == '-')
positive = true;
else
num = num * 10 + (c - '0');
}
}
return cur;
}
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