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/**
 * Returns a hash code for this string. The hash code for a
 * <code>String</code> object is computed as
 * <blockquote><pre>
 * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
 * </pre></blockquote>
 * using <code>int</code> arithmetic, where <code>s[i]</code> is the
 * <i>i</i>th character of the string, <code>n</code> is the length of
 * the string, and <code>^</code> indicates exponentiation.
 * (The hash value of the empty string is zero.)
 *
 * @return  a hash code value for this object.
 */
public int hashCode() {
    int h = hash;
    if (h == 0 && value.length > 0) {
        char val[] = value;

        for (int i = 0; i < value.length; i++) {
            h = 31 * h + val[i];
        }
        hash = h;
    }
    return h;
}

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function hashCode($str) {  
    $h = 0;
    $len = strlen($str);
    $t = 2147483648; //java int的最大值
    for ($i = 0; $i < $len; $i++) {
        $h = (($h << 5) - $h) + ord($str[$i]);
        if($h > $t) $h %= $t; //溢出取模
    }
    return $h;
}

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$arr_src = ['at','bU','c6']; 
$str_tmp = '';  //存储临时字符串
$arr_rtn = [];
$t = combs(11,$arr_src,$str_tmp,$arr_rtn);
/**
 * 组合算法
 **/
function combs($n,$arr,$str,&$arr_rtn) {
    if($n==1){
        for($j=0;$j<3;$j++){
            $arr_rtn[$str.$arr[$j]] = 0;
        }
    }else
    {
        for($j=0;$j<3;$j++){
            combs($n-1,$arr,$str.$arr[$j],$arr_rtn);
        }
    }
}
$json = json_encode($arr_rtn);
file_put_contents('log/times31.txt',$json);

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{
	"atatatatatatatatatatat":0,
	"atatatatatatatatatatbU":0,
	"atatatatatatatatatatc6":0,
	"atatatatatatatatatbUat":0,
	"atatatatatatatatatbUbU":0,
	"atatatatatatatatatbUc6":0,
	"atatatatatatatatatc6at":0,
	"atatatatatatatatatc6bU":0,
	"atatatatatatatatatc6c6":0,
	"atatatatatatatatbUatat":0,
	"atatatatatatatatbUatbU":0,
	"atatatatatatatatbUatc6":0,
	"atatatatatatatatbUbUat":0,
	"atatatatatatatatbUbUbU":0,
	"atatatatatatatatbUbUc6":0,
	"atatatatatatatatbUc6at":0
}

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public class IndexController {

    @RequestMapping(value="/",method = RequestMethod.GET)
    public String index(){

        String jsonStr = "";
        try
        {
            FileReader fr = new FileReader("times31.txt");//需要读取的文件路径
            BufferedReader br = new BufferedReader(fr);
            jsonStr = br.readLine();
            br.close();//关闭BufferReader流
            fr.close();		//关闭文件流
        }catch(IOException e)//捕捉异常
        {
            System.out.println("指定文件不存在");//处理异常
        }

        Map<String, Object> map = new HashMap<String, Object>();

        map = JSONObject.fromObject(jsonStr);

        return "Hash Collision ~";
    }
}