参考文档 http://php.net/manual/zh/function.array-keys.php
首个下标 array_search
多个下标 array_keys 配合可选参数 search_value 完成
eg：
<?php function showIndex($source_arr, $sum) { $index_list = []; $pass_index_list = []; foreach ($source_arr as $index => $value) { // filter repeat index if (in_array($value, $pass_index_list)) { continue; } // search another index $diff = $sum - $value; $ano_index = array_keys($source_arr, $diff); if (!$ano_index) { continue; } foreach ($ano_index as $choose_index) { $index_list[] = [$index,$choose_index]; } // set repeat index $pass_index_list[] = $diff; } return $index_list; } // run function $source_arr = [49, 1, 2, 3, 50, 50,49,49, 51]; //$source_arr = [49, 1, 2, 3, 50, 51]; $sum = 99; print_r(showIndex($source_arr, $sum));