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27-PossibleBipartition.java
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27-PossibleBipartition.java
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class Solution {
boolean ans = true;
boolean[] visited;
int N;
int[] levels;
public boolean possibleBipartition(int N, int[][] dislikes) {
int[][] adjMat = new int[N + 1][N + 1];
this.visited = new boolean[N + 1];
this.N = N;
this.levels = new int[N + 1];
int row = dislikes.length;
if (row == 0) return true;
HashMap<Integer, ArrayList<Integer>> adjList = new HashMap<>();
//build the adjList
for (int i = 0; i < row; i++) {
int x = dislikes[i][0];
int y = dislikes[i][1];
ArrayList<Integer> xl = adjList.getOrDefault(x, new ArrayList<Integer>());
ArrayList<Integer> yl = adjList.getOrDefault(y, new ArrayList<Integer>());
xl.add(y);
adjList.put(x, xl);
yl.add(x);
adjList.put(y, yl);
}
// System.out.print(adjList.toString());
for (int i = 1; i < N + 1; i++) {
if (!visited[i])
dfs(adjList, i, 0, 1);
}
return ans;
}
public void dfs(HashMap<Integer, ArrayList<Integer>> adjMat, int vertex, int parent, int level) {
if (!ans) return;
visited[vertex] = true;
levels[vertex] = level;
ArrayList<Integer> edges = adjMat.getOrDefault(vertex, new ArrayList<Integer>());
for (int neighbour : edges) {
if (neighbour == parent) continue;
if (!visited[neighbour]) {
dfs(adjMat, neighbour, vertex, level + 1);
} else {
if ((level - levels[neighbour]) % 2 == 0) {
ans = false;
}
}
}
}
}
// adjMat
// 0 0 0 0
// 0 0 1 1
// 0 1 0 1
// 0 1 1 0
// 1->2->3->4->5->1