最大匹配（PHP）

    // maximum matching algorithm
    // unweighted bipartite graph
    // dfs hungarian algorithm

    function dfs($bigraph, $u, &$path, &$matching){
        foreach($bigraph[$u] as $v){
            if(!isset($path[$v])){      // not in path already
                $path[$v] = true;
                if(!isset($matching[$v]) || dfs($bigraph, $matching[$v], $path, $matching)){
                    // not matching node, the path is agumenting path, switch path, and return true
                    $matching[$v] = $u;
                    $matching[$u] = $v;
                    return true;
                }
            }
        }

        return false;                   // not agumenting path
    }

    function hungarian($bigraph){
        $matching = [];

        foreach($bigraph as $u=>$x){
            if(!isset($matching[$u])){  // not a matching node
                $path = [];             // save the nodes in path
                dfs($bigraph, $u, $path, $matching);
            }
        }

        return array_intersect_key($matching, $bigraph);
    }

    // left node idx is key
    // right nodes is value
    // eg. left nodes: 0 - 4, right nodes = 5 - 9
    $bigraph = [0 => [6, 9], 1 => [7], 2 => [6, 8], 3 => [8, 9], 4 => [5, 7]];
    $r = hungarian($bigraph);
    print_r($r);
?>