Solution.java

/**
 * // 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 empty list if this NestedInteger holds a single integer
 *     public List<NestedInteger> getList();
 * }
 */
class Solution {
    public NestedInteger deserialize(String s) {
        if ("".equals(s)) {
            return new NestedInteger();
        }
        if (s.charAt(0) != '[') {
            return new NestedInteger(Integer.parseInt(s));
        }
        if (s.length() <= 2) {
            return new NestedInteger();
        }
        NestedInteger ans = new NestedInteger();
        int depth = 0;
        for (int i = 1, j = 1; i < s.length(); ++i) {
            if (depth == 0 && (s.charAt(i) == ',' || i == s.length() - 1)) {
                ans.add(deserialize(s.substring(j, i)));
                j = i + 1;
            } else if (s.charAt(i) == '[') {
                ++depth;
            } else if (s.charAt(i) == ']') {
                --depth;
            }
        }
        return ans;
    }
}