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php实现lzw压缩

2026-02-28 00:07:48PHP

LZW压缩算法简介

LZW（Lempel-Ziv-Welch）是一种基于字典的无损压缩算法，广泛用于GIF图像格式和早期文件压缩。其核心思想是将输入的字符串序列映射为固定长度的编码，通过动态构建字典实现压缩。

PHP实现LZW压缩

以下是一个基础的PHP实现示例，包含压缩和解压两部分：

php实现lzw压缩

压缩函数实现

function lzw_compress($string) {
    $dict = array();
    for ($i = 0; $i < 256; $i++) {
        $dict[chr($i)] = $i;
    }

    $current = "";
    $result = array();
    $dict_size = 256;

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

        if (isset($dict[$combined])) {
            $current = $combined;
        } else {
            $result[] = $dict[$current];
            $dict[$combined] = $dict_size++;
            $current = $char;
        }
    }

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

    return $result;
}

解压函数实现

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

    $current = chr($compressed[0]);
    $result = $current;
    $dict_size = 256;

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

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

        $result .= $entry;
        $dict[$dict_size++] = $current . $entry[0];
        $current = $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";