https://leetcode.com/contest/leetcode-weekly-contest-36/problems/design-compressed-string-iterator/

compressed_string_iterator.cpp

class StringIterator {
public:
    StringIterator(string compressedString) : compressedString(compressedString) {
        size_t i = 0;
        while (i < compressedString.size()) {
            freqTable.push_back(make_pair(compressedString[i++], 0));
            int freq = 0;
            while (i < compressedString.size() && isdigit(compressedString[i])) {
                freq = (freq * 10) + (compressedString[i] - '0');
                i++;
            }
            freqTable.back().second += freq;
        }
    }
    
    char next() {
        if (!hasNext()) {
            return ' ';
        }
        char c = freqTable[idx].first;
        freqTable[idx].second--;
        if (freqTable[idx].second == 0) {
            idx++;
        }
        return c;
    }
    
    bool hasNext() {
        return idx < freqTable.size();
    }
    size_t idx = 0;
    string compressedString;
    vector<pair<char, int>> freqTable;
};

/**
 * 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();
 */