数据库有十万条数据,比较的规则是,第一条和第二条后面的所有数据进行比较,第二条和后第三条后面的所有数据进行比较,以此类推。。。比较所有的数据.不想使用多重循环,想在一个循环内全部搞定,请问有比较好的算法吗?
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数据库有十万条数据,比较的规则是,第一条和第二条后面的所有数据进行比较,第二条和后第三条后面的所有数据进行比较,以此类推。。。比较所有的数据.不想使用多重循环,想在一个循环内全部搞定,请问有比较好的算法吗?
看到你的场景说是,找重复。
SELECT id from table GROUP BY id HAVING COUNT(*)>1
这样获取回来的就是含重复数据。
如果是如题所说的两两比较,如果限定 "两两比较" 必然是 O(n^2),既然确定了时间复杂度,那么就不用算法效率了。剩下的就是考虑在那计算了。
如果数据规模不够大,内存里计算完全可以了,前提是数据规模不大。
详述场景~~~~~~~~~~~~~~~~
先排序,后比较
不建议在数据库中操作,最方便的就是把这10w 条数据取出来,放到 php 内存中来操作.
代码如下
<code>$sql = "select id,data from table order by data asc"; $result = [ 0=> ['id'=>3, 'data'=>1], 1=> ['id'=>1, 'data'=>2], 2=> ['id'=>4, 'data'=>2], 3=> ['id'=>5, 'data'=>2], 4=> ['id'=>2, 'data'=>5], ]; //遍历小于 //小于当前元素下标的元素 //遍历大于 //大于当前元素下标的元素 //相同,有点复杂,代码如下 $same = array(); $current = 0; $next = $current + 1; //遍历一遍数组 while(isset($result[ $next ])) { $data = $result[ $current ][ 'data' ]; //如果当前元素值和下一个元素值一样,放到值数组中 if ($data == $result[ $next ][ 'data' ]) { $same[ $data ][] = $result[ $next ]; $next ++; }else{ //如果不一样,当前元素指向 当下标为$next的元素 $current = $next; $next = $current+1; } } var_export($same); //结果 array ( 2 => array ( 0 => array ( 'id' => 4, 'data' => 2, ), 1 => array ( 'id' => 5, 'data' => 2, ), ), ) </code>
有几个问题是需要注意的:
1,数据要在内存中做排序或对比,不要在数据库内执行;
2,两两比较的目的是什么?要从这10W+数据中取出最大的N个?还是做排序?建议在内存中用一个索引数组存储排序后的所有数据;
3,排序算法使用快排;

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