{"componentChunkName":"component---src-templates-blog-js","path":"/blog/algorithm/algo_20200320_6/","result":{"data":{"markdownRemark":{"html":"

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Undirected Graph에서 Minimum Spanning Tree (MST) 구하기.

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Kruskal Algorithm을 사용.

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Kruskal Algorithm :

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  1. 모든 edge와 가중치를 Priority Queue에 저장한다. (가중치가 작은 순으로 정렬)
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  2. 모든 노드의 부모 노드 (parent[])를 자기 자신으로 초기화한다.
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    전체 노드가 N개일 때 while 문을 N-1번 반복하면서, (MST는 Tree이고, Tree의 edge개수는 N-1이므로)

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Java Code

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import java.util.Comparator;\nimport java.util.PriorityQueue;\nimport java.util.Scanner;\n\nclass Edge_PS {\n    int a, b;\n    int w;\n    Edge_PS(int a, int b, int w) {\n        this.a = a; this.b = b; this.w = w;\n    }\n}\n\npublic class Main {\n    static Scanner in = new Scanner(System.in);\n    static int n, m;\n    static StringBuilder sb = new StringBuilder();\n    static int[] parent, visited;\n    static PriorityQueue<Edge_PS> pq = new PriorityQueue<>(new Comparator<Edge_PS>() {\n        @Override\n        public int compare(Edge_PS o1, Edge_PS o2) {\n            return o1.w-o2.w;\n        }\n    });\n    public static void main(String[] args) {\n        while (true) {\n            n = in.nextInt(); m = in.nextInt();\n            if(n==0&& m==0) break;\n            long total = 0, minimum = 0;\n//            여러 개의 테스트케이스를 받아야 하므로 필요한 배열, Queue를 반드시 초기화해야 한다.\n            visited = new int[n];\n            parent = new int[n];\n            pq.clear();\n            while (m-- >0){\n                int a = in.nextInt(); int b = in.nextInt(); int w = in.nextInt();\n                pq.add(new Edge_PS(a, b, w));\n                parent[a] = a; parent[b] = b;\n                total+=w;\n            }\n            int cnt = 0;\n            while (cnt<n-1) {\n                Edge_PS curr = pq.poll();\n                if(union(curr.a, curr.b)) {\n                    minimum += curr.w;\n                    cnt++;\n                }\n            }\n            sb.append((total-minimum)+\"\\n\");\n        }\n        System.out.println(sb.toString());\n    }\n    public static boolean union(int a, int b) {\n        int aRoot = findRoot(a), bRoot = findRoot(b);\n        if(aRoot==bRoot) return false;\n        else {\n            parent[bRoot] = aRoot;\n            return true;\n        }\n    }\n    public static int findRoot(int a) {\n        if(parent[a]==a) return a;\n        else {\n            return findRoot(parent[a]);\n        }\n    }\n}
","id":"a2942fca-afa3-5751-b808-186197aaf45d","frontmatter":{"title":"[Algorithm] 백준 6497 : 전력난 ","date":"2020-03-20T00:00:00.000Z","description":null},"fields":{"slug":"/blog/algorithm/algo_20200320_6/"}}},"pageContext":{"slug":"/blog/algorithm/algo_20200320_6/"}}}