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.
题目难以理解，参考点击打开链接，程序如下：
/**
* // 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) {
if (s == null) {
return null;
}
Stack<NestedInteger> stack = new Stack<>();
stack.push(new NestedInteger());
char sign = '+';
Integer num = null;
for (int i = 0; i <= s.length(); ++i) {
char c = i == s.length() ? ',' : s.charAt(i);
if (c == '-') {
sign = '-';
} else if (Character.isDigit(c)) {
num = (num == null ? 0 : num) * 10 + c - '0';
} else if (c == '[') {
stack.push(new NestedInteger());
} else {
if (num != null) {
stack.peek().add(new NestedInteger(sign == '+' ? num : -num));
}
num = null;
sign = '+';
if (c == ']') {
NestedInteger cur = stack.pop();
stack.peek().add(cur);
}
}
}
return stack.pop().getList().get(0);
}
}