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php实现lzw压缩

2026-02-14 01:11:44PHP

LZW压缩算法简介

LZW（Lempel-Ziv-Welch）是一种无损数据压缩算法，广泛应用于GIF图像格式和UNIX压缩工具。其核心思想是利用字典动态编码重复出现的字符串。

PHP实现LZW压缩基础步骤

初始化字典 创建包含所有单字符的初始字典，键为字符，值为对应编码：

php实现lzw压缩

$dictionary = array();
for ($i = 0; $i < 256; $i++) {
    $dictionary[chr($i)] = $i;
}

压缩过程实现

php实现lzw压缩

function lzw_compress($string) {
    global $dictionary;
    $result = array();
    $current = "";

    for ($i = 0; $i < strlen($string); $i++) {
        $char = $string[$i];
        $combined = $current . $char;

        if (isset($dictionary[$combined])) {
            $current = $combined;
        } else {
            $result[] = $dictionary[$current];
            $dictionary[$combined] = count($dictionary);
            $current = $char;
        }
    }

    if ($current !== "") {
        $result[] = $dictionary[$current];
    }

    return $result;
}

解压过程实现

function lzw_decompress($compressed) {
    $dictionary = array();
    for ($i = 0; $i < 256; $i++) {
        $dictionary[$i] = chr($i);
    }

    $result = "";
    $prev = $dictionary[$compressed[0]];
    $result .= $prev;

    for ($i = 1; $i < count($compressed); $i++) {
        $code = $compressed[$i];

        if (isset($dictionary[$code])) {
            $entry = $dictionary[$code];
        } else {
            $entry = $prev . $prev[0];
        }

        $result .= $entry;
        $dictionary[count($dictionary)] = $prev . $entry[0];
        $prev = $entry;
    }

    return $result;
}

使用示例

$original = "TOBEORNOTTOBEORTOBEORNOT";
$compressed = lzw_compress($original);
$decompressed = lzw_decompress($compressed);

echo "Original: " . $original . "\n";
echo "Compressed: " . implode(',', $compressed) . "\n";
echo "Decompressed: " . $decompressed . "\n";