def run_length_encode(data):
    """ランレングス圧縮を行う関数"""
    if not data:
        return ""
    
    encoded = []
    count = 1
    current = data[0]
    
    for i in range(1, len(data)):
        if data[i] == current:
            count += 1
        else:
            encoded.append(f"{current}{count}")
            current = data[i]
            count = 1
    
    encoded.append(f"{current}{count}")
    return "".join(encoded)

def run_length_decode(data):
    """ランレングス圧縮を展開する関数"""
    decoded = []
    i = 0
    
    while i < len(data):
        char = data[i]
        i += 1
        count_str = ""
        
        while i < len(data) and data[i].isdigit():
            count_str += data[i]
            i += 1
        
        count = int(count_str) if count_str else 1
        decoded.append(char * count)
    
    return "".join(decoded)

# 使用例
original = "AAAAAABBBCCCCCCDAA"
compressed = run_length_encode(original)
print(f"圧縮前: {original}")
print(f"圧縮後: {compressed}")
print(f"展開後: {run_length_decode(compressed)}")

function runLengthEncode(data) {
    if (!data) return "";
    
    let encoded = "";
    let count = 1;
    let current = data[0];
    
    for (let i = 1; i < data.length; i++) {
        if (data[i] === current) {
            count++;
        } else {
            encoded += current + count;
            current = data[i];
            count = 1;
        }
    }
    
    encoded += current + count;
    return encoded;
}

function runLengthDecode(data) {
    let decoded = "";
    let i = 0;
    
    while (i < data.length) {
        const char = data[i];
        i++;
        let countStr = "";
        
        while (i < data.length && !isNaN(data[i])) {
            countStr += data[i];
            i++;
        }
        
        const count = parseInt(countStr) || 1;
        decoded += char.repeat(count);
    }
    
    return decoded;
}