[Leetcode] 604. Design Compressed String Iterator 解题报告

题目：

Design and implement a data structure for a compressed string iterator. It should support the following operations: next and hasNext.

The given compressed string will be in the form of each letter followed by a positive integer representing the number of this letter existing in the original uncompressed string.

next() - if the original string still has uncompressed characters, return the next letter; Otherwise return a white space.
hasNext() - Judge whether there is any letter needs to be uncompressed.

Note:
Please remember to RESET your class variables declared in StringIterator, as static/class variables are persisted across multiple test cases. Please see here for more details.

Example:

StringIterator iterator = new StringIterator("L1e2t1C1o1d1e1");

iterator.next(); // return 'L'
iterator.next(); // return 'e'
iterator.next(); // return 'e'
iterator.next(); // return 't'
iterator.next(); // return 'C'
iterator.next(); // return 'o'
iterator.next(); // return 'd'
iterator.hasNext(); // return true
iterator.next(); // return 'e'
iterator.hasNext(); // return false
iterator.next(); // return ' '

思路：

由于一个字符的出现次数可能大于9次，所以我们用istringstream对compressedString进行解析，将字母和其对应的出现次数分别存储在两个数组中。判断hasNext的方法就是看当前的index是否已经到达了数组的末尾。而对于next函数而言，需要首先判断是否hasNext，如果是，则返回对应字符；否则就返回空格。

代码：

class StringIterator {
public:
    StringIterator(string compressedString) {
        chars.clear();
        counts.clear();
        index = 0;
        count = 0;
        istringstream iss(compressedString);
        char c;
        int count;
        while (!iss.eof()) {
            iss >> c;
            iss >> count;
            chars.push_back(c);
            counts.push_back(count);
        }
    }
    
    char next() {
        if (hasNext()) {
            ++count;
            return chars[index];
        }
        else {
            return ' ';
        }
    }
    
    bool hasNext() {
        if (count == counts[index]) {
            ++index;
            count = 0;
        }
        return index < chars.size();
    }
private:
    vector chars;
    vector counts;
    int index;
    int count;
};

/**
 * Your StringIterator object will be instantiated and called as such:
 * StringIterator obj = new StringIterator(compressedString);
 * char param_1 = obj.next();
 * bool param_2 = obj.hasNext();
 */