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143
...ode_java/src/main/java/LeetCodeJava/Graph/NumberOfConnectedComponentsUndirectedGraph.java
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,143 @@ | ||
| package LeetCodeJava.Graph; | ||
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| // https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/description/?envType=list&envId=xoqag3yj | ||
| // https://leetcode.ca/all/323.html | ||
| // https://leetcode.ca/2016-10-18-323-Number-of-Connected-Components-in-an-Undirected-Graph/ | ||
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| import java.util.*; | ||
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| public class NumberOfConnectedComponentsUndirectedGraph { | ||
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| // V0 | ||
| // IDEA : GRAPH | ||
| // TODO : implement it | ||
| // public int countComponents(int n, int[][] edges) { | ||
| // return 0; | ||
| // } | ||
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| // V1 | ||
| // IDEA : UNION FIND | ||
| // https://leetcode.ca/2016-10-18-323-Number-of-Connected-Components-in-an-Undirected-Graph/ | ||
| private int[] p; | ||
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| public int countComponents_1(int n, int[][] edges) { | ||
| p = new int[n]; | ||
| for (int i = 0; i < n; ++i) { | ||
| p[i] = i; | ||
| } | ||
| for (int[] e : edges) { | ||
| int a = e[0], b = e[1]; | ||
| p[find(a)] = find(b); | ||
| } | ||
| int ans = 0; | ||
| for (int i = 0; i < n; ++i) { | ||
| if (i == find(i)) { | ||
| ++ans; | ||
| } | ||
| } | ||
| return ans; | ||
| } | ||
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| private int find(int x) { | ||
| if (p[x] != x) { | ||
| p[x] = find(p[x]); | ||
| } | ||
| return p[x]; | ||
| } | ||
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| // V2 | ||
| // IDEA : DFS | ||
| // https://www.cnblogs.com/cnoodle/p/14197652.html | ||
| public int countComponents_2(int n, int[][] edges) { | ||
| int count = 0; | ||
| List<List<Integer>> g = new ArrayList<>(); | ||
| boolean[] visited = new boolean[n]; | ||
| for (int i = 0; i < n; i++) { | ||
| g.add(new ArrayList<>()); | ||
| } | ||
| for (int[] e : edges) { | ||
| g.get(e[0]).add(e[1]); | ||
| g.get(e[1]).add(e[0]); | ||
| } | ||
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| for (int i = 0; i < n; i++) { | ||
| if (!visited[i]) { | ||
| count++; | ||
| dfs(visited, i, g); | ||
| } | ||
| } | ||
| return count; | ||
| } | ||
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| private void dfs(boolean[] visited, int node, List<List<Integer>> g) { | ||
| visited[node] = true; | ||
| for (int next : g.get(node)) { | ||
| if (!visited[next]) { | ||
| dfs(visited, next, g); | ||
| } | ||
| } | ||
| } | ||
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| // V3 | ||
| // IDEA : UNION FIND | ||
| // https://www.cnblogs.com/cnoodle/p/14197652.html | ||
| public int countComponents_3(int n, int[][] edges) { | ||
| int count = n; | ||
| int[] parents = new int[n]; | ||
| for (int i = 0; i < n; i++) { | ||
| parents[i] = i; | ||
| } | ||
| for (int[] edge : edges) { | ||
| int p = find(parents, edge[0]); | ||
| int q = find(parents, edge[1]); | ||
| if (p != q) { | ||
| parents[p] = q; | ||
| count--; | ||
| } | ||
| } | ||
| return count; | ||
| } | ||
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| private int find(int[] parents, int i) { | ||
| while (parents[i] != i) { | ||
| parents[i] = parents[parents[i]]; // route compression | ||
| i = parents[i]; | ||
| } | ||
| return i; | ||
| } | ||
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| // V4 | ||
| // IDEA : BFS | ||
| // https://www.cnblogs.com/cnoodle/p/14197652.html | ||
| public int countComponents_4(int n, int[][] edges) { | ||
| int count = 0; | ||
| List<List<Integer>> g = new ArrayList<>(); | ||
| boolean[] visited = new boolean[n]; | ||
| for (int i = 0; i < n; i++) { | ||
| g.add(new ArrayList<>()); | ||
| } | ||
| for (int[] e : edges) { | ||
| g.get(e[0]).add(e[1]); | ||
| g.get(e[1]).add(e[0]); | ||
| } | ||
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| for (int i = 0; i < n; i++) { | ||
| if (!visited[i]) { | ||
| count++; | ||
| Queue<Integer> queue = new LinkedList<>(); | ||
| queue.offer(i); | ||
| while (!queue.isEmpty()) { | ||
| int index = queue.poll(); | ||
| visited[index] = true; | ||
| for (int next : g.get(index)) { | ||
| if (!visited[next]) { | ||
| queue.offer(next); | ||
| } | ||
| } | ||
| } | ||
| } | ||
| } | ||
| return count; | ||
| } | ||
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| } |