LeetCode-in-Java

3243. Shortest Distance After Road Addition Queries I

Medium

You are given an integer n and a 2D integer array queries.

There are n cities numbered from 0 to n - 1. Initially, there is a unidirectional road from city i to city i + 1 for all 0 <= i < n - 1.

queries[i] = [ui, vi] represents the addition of a new unidirectional road from city ui to city vi. After each query, you need to find the length of the shortest path from city 0 to city n - 1.

Return an array answer where for each i in the range [0, queries.length - 1], answer[i] is the length of the shortest path from city 0 to city n - 1 after processing the first i + 1 queries.

Example 1:

Input: n = 5, queries = [[2,4],[0,2],[0,4]]

Output: [3,2,1]

Explanation:

After the addition of the road from 2 to 4, the length of the shortest path from 0 to 4 is 3.

After the addition of the road from 0 to 2, the length of the shortest path from 0 to 4 is 2.

After the addition of the road from 0 to 4, the length of the shortest path from 0 to 4 is 1.

Example 2:

Input: n = 4, queries = [[0,3],[0,2]]

Output: [1,1]

Explanation:

After the addition of the road from 0 to 3, the length of the shortest path from 0 to 3 is 1.

After the addition of the road from 0 to 2, the length of the shortest path remains 1.

Constraints:

• 3 <= n <= 500
• 1 <= queries.length <= 500
• queries[i].length == 2
• 0 <= queries[i][0] < queries[i][1] < n
• 1 < queries[i][1] - queries[i][0]
• There are no repeated roads among the queries.

Solution

import java.util.ArrayList;

@SuppressWarnings("unchecked")
public class Solution {
    public int[] shortestDistanceAfterQueries(int n, int[][] queries) {
        int[] dist = new int[n];
        for (int i = 0; i < n; i++) {
            dist[i] = i;
        }
        ArrayList<Integer>[] parent = new ArrayList[n];
        for (int i = 0; i < n; i++) {
            parent[i] = new ArrayList<>();
            if (i != n - 1) {
                parent[i].add(i + 1);
            }
        }
        int[] ans = new int[queries.length];
        for (int i = 0; i < queries.length; i++) {
            int u = queries[i][0];
            int v = queries[i][1];
            if (dist[v] > dist[u] + 1) {
                dist[v] = dist[u] + 1;
                parent[u].add(v);
                updateDistance(v, dist, parent);
            } else {
                parent[u].add(v);
            }
            ans[i] = dist[n - 1];
        }
        return ans;
    }

    public void updateDistance(int par, int[] dist, ArrayList<Integer>[] parent) {
        for (int i = 0; i < parent[par].size(); i++) {
            int child = parent[par].get(i);
            if (dist[child] > dist[par] + 1) {
                dist[child] = dist[par] + 1;
                updateDistance(child, dist, parent);
            }
        }
    }
}

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