Formatted question description: https://leetcode.ca/all/1782.html

1782. Count Pairs Of Nodes

Level

Hard

Description

You are given an undirected graph represented by an integer n, which is the number of nodes, and edges, where edges[i] = [u_i, v_i] which indicates that there is an undirected edge between u_i and v_i. You are also given an integer array queries.

The answer to the j-th query is the number of pairs of nodes (a, b) that satisfy the following conditions:

  • a < b
  • cnt is strictly greater than queries[j], where cnt is the number of edges incident to a or b.

Return an array answers such that answers.length == queries.length and answers[j] is the answer of the j-th query.

Note that there can be repeated edges.

Example 1:

Image text

Input: n = 4, edges = [[1,2],[2,4],[1,3],[2,3],[2,1]], queries = [2,3]

Output: [6,5]

Explanation: The number of edges incident to at least one of each pair is shown above.

Example 2:

Input: n = 5, edges = [[1,5],[1,5],[3,4],[2,5],[1,3],[5,1],[2,3],[2,5]], queries = [1,2,3,4,5]

Output: [10,10,9,8,6]

Constraints:

  • 2 <= n <= 2 * 10^4
  • 1 <= edges.length <= 10^5
  • 1 <= u_i, v_i <= n
  • u_i != v_i
  • 1 <= queries.length <= 20
  • 0 <= queries[j] < edges.length

Solution

First, calculate the degrees of each node and the counts of each edge. Next, use another array arr to store the degrees and sort arr. Then, for each query, use two pointers to calculate the number of pairs of nodes that satisfy the conditions. Finally, return the query result.

  • class Solution {
        public int[] countPairs(int n, int[][] edges, int[] queries) {
            final int FACTOR = 100000;
            int[] degrees = new int[n + 1];
            int[] arr = new int[n + 1];
            int length = queries.length;
            int[] pairs = new int[length];
            Map<Integer, Integer> map = new HashMap<Integer, Integer>();
            for (int[] edge : edges) {
                int u = Math.min(edge[0], edge[1]);
                int v = Math.max(edge[0], edge[1]);
                degrees[u]++;
                degrees[v]++;
                int key = u * FACTOR + v;
                map.put(key, map.getOrDefault(key, 0) + 1);
            }
            for (int i = 1; i <= n; i++)
                arr[i] = degrees[i];
            Arrays.sort(arr);
            for (int i = 0; i < length; i++) {
                int low = 1, high = n;
                while (low < high) {
                    while (low < high && arr[low] + arr[high] <= queries[i])
                        low++;
                    if (low < high)
                        pairs[i] += high - low;
                    high--;
                }
                if (pairs[i] != 0) {
                    Set<Integer> visited = new HashSet<Integer>();
                    for (int[] edge : edges) {
                        int u = Math.min(edge[0], edge[1]);
                        int v = Math.max(edge[0], edge[1]);
                        int key = u * FACTOR + v;
                        if (visited.add(key)) {
                            int pair = degrees[u] + degrees[v] - map.get(key);
                            if (degrees[u] + degrees[v] > queries[i] && pair <= queries[i])
                                pairs[i]--;
                        }
                    }
                }
            }
            return pairs;
        }
    }
    
  • Todo
    
  • print("Todo!")
    

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