Problem:
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Minimum Spanning Tree

For a given weighted graph $G = (V, E)$, find the minimum spanning tree (MST) of $G$ and print total weight of edges belong to the MST.

Input

In the first line, an integer $n$ denoting the number of vertices in $G$ is given. In the following $n$ lines, a $n \times n$ adjacency matrix $A$ which represents $G$ is given.
$a_{ij}$ denotes the weight of edge connecting vertex $i$ and vertex $j$. If there is no edge between $i$ and $j$, $a_{ij}$ is given by -1.

Output

Print the total weight of the minimum spanning tree of $G$.

Constraints

$1 \leq n \leq 100$

$0 \leq a_{ij} \leq 2,000$ (if $a_{ij} \neq -1$)

$a_{ij} = a_{ji}$

$G$ is a connected graph

Sample Input 1

5
-1 2 3 1 -1
2 -1 -1 4 -1
3 -1 -1 1 1
1 4 1 -1 3
-1 -1 1 3 -1

Sample Output 1

5

Reference

Introduction to Algorithms, Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, and Clifford Stein. The MIT Press.

Solution in Scala (judge verdict: Accepted)

import scala.io.StdIn.{readInt, readLine};
import scala.annotation.tailrec;
object Main {
    def main(args: Array[String]): Unit = {
        val size = readInt;
        val m = new Array[Array[Int]](size);
        (0 until size).foreach {  i => m(i) = readLine.trim.split(" ").map( a => if (a.toInt == -1) Int.MaxValue else a.toInt)}
        val g = new Graph(size, m);
        println(g.prim.sum);
    }
}
case class Graph(size: Int, matrix: Array[Array[Int]]) {
    val INFINITY = Int.MaxValue
    def prim(): Array[Int] = {
        // WHITE : 未訪問, GRAY: MST候補ノード, BLACK: MST追加済みノード
        val WHITE = 0; val GRAY = 1; val BLACK = 2;
        val color = new Array[Int](size); // 訪問状態リスト(WHITE, GRAY, BLACK)
        val distance = new Array[Int](size).map( e => INFINITY); //  重みリスト
        @tailrec
        def _prim(curr: Int): Unit = {
            // MSTに属する頂点の集合から最も近いノードの index を取得する
            val idx = (0 until size).foldLeft(-1) { (minidx, i) =>
                if (color(i) == BLACK) {
                    // すでにMSTに追加されているノードは評価しない
                    minidx;
                } else { // color(i) == GRAY or WHITE
                    // curr の子ノードをMST候補ノードに追加
                    if (matrix(curr)(i) != -1) color(i) = GRAY;
                    if (color(i) == GRAY) {
                        // すでに登録されている重みよりも curr からの重みのほうが小さい場合は親ノードと重みを更新する
                        if (matrix(curr)(i) < distance(i)) distance(i) = matrix(curr)(i);
                        if (minidx == -1 || distance(i) < distance(minidx)) i else minidx;
                    } else { // color(i) == WHITE
                        // 現時点でMSTに隣接していないノードは評価しない
                        minidx;
                    }
                }
            }
            if (idx != -1){
                // MSTから最も距離の近いノードを追加
                color(idx) = BLACK;
                _prim(idx);
            }
        }
        distance(0) = 0;
        color(0) = BLACK;
        _prim(0);
        distance;
    }
}