LeetCode in Kotlin
2699. Modify Graph Edge Weights
Hard
You are given an undirected weighted connected graph containing n nodes labeled from 0 to n - 1, and an integer array edges where edges[i] = [ai, bi, wi] indicates that there is an edge between nodes ai and bi with weight wi.
Some edges have a weight of -1 (wi = -1), while others have a positive weight (wi > 0).
Your task is to modify all edges with a weight of -1 by assigning them positive integer values in the range [1, 2 * 109] so that the shortest distance between the nodes source and destination becomes equal to an integer target. If there are multiple modifications that make the shortest distance between source and destination equal to target, any of them will be considered correct.
Return an array containing all edges (even unmodified ones) in any order if it is possible to make the shortest distance from source to destination equal to target, or an empty array if it’s impossible.
Note: You are not allowed to modify the weights of edges with initial positive weights.
Example 1:
Input: n = 5, edges = [[4,1,-1],[2,0,-1],[0,3,-1],[4,3,-1]], source = 0, destination = 1, target = 5
Output: [[4,1,1],[2,0,1],[0,3,3],[4,3,1]]
Explanation: The graph above shows a possible modification to the edges, making the distance from 0 to 1 equal to 5.
Example 2:
Input: n = 3, edges = [[0,1,-1],[0,2,5]], source = 0, destination = 2, target = 6
Output: []
Explanation: The graph above contains the initial edges. It is not possible to make the distance from 0 to 2 equal to 6 by modifying the edge with weight -1. So, an empty array is returned.
Example 3:
Input: n = 4, edges = [[1,0,4],[1,2,3],[2,3,5],[0,3,-1]], source = 0, destination = 2, target = 6
Output: [[1,0,4],[1,2,3],[2,3,5],[0,3,1]]
Explanation: The graph above shows a modified graph having the shortest distance from 0 to 2 as 6.
Constraints:
1 <= n <= 1001 <= edges.length <= n * (n - 1) / 2edges[i].length == 30 <= ai, bi < nwi = -1or1 <= wi <= 107ai != bi0 <= source, destination < nsource != destination1 <= target <= 109- The graph is connected, and there are no self-loops or repeated edges
Solution
import java.util.PriorityQueue
class Solution {
private inner class Edge(var s: Int, var d: Int, var wt: Int)
private lateinit var g: Array<ArrayList<Edge>?>
private var n = 0
private var t = 0
fun modifiedGraphEdges(
n: Int,
edges: Array<IntArray>,
source: Int,
destination: Int,
target: Int,
): Array<IntArray> {
this.n = n
g = arrayOfNulls(n)
t = target
for (i in 0 until n) {
g[i] = ArrayList()
}
for (e in edges) {
val s = e[0]
val d = e[1]
val wt = e[2]
if (wt == -1) continue
g[s]!!.add(Edge(s, d, wt))
g[d]!!.add(Edge(d, s, wt))
}
val inc = shortestPath(source, destination)
if (inc != -1 && inc < target) return Array(0) { IntArray(0) }
if (inc == target) {
ntomax(edges)
return edges
}
for (e in edges) {
if (e[2] == -1) {
e[2] = 1
val s = e[0]
val d = e[1]
val wt = e[2]
g[s]!!.add(Edge(s, d, wt))
g[d]!!.add(Edge(d, s, wt))
val cost = shortestPath(source, destination)
if (cost == -1) continue
if (cost < target) {
e[2] = target - cost + 1
ntomax(edges)
return edges
}
if (cost == target) {
ntomax(edges)
return edges
}
}
}
return Array(0) { IntArray(0) }
}
private fun ntomax(edges: Array<IntArray>) {
for (e in edges) {
if (e[2] == -1) {
e[2] = 1000000000
}
}
}
private inner class Pair(var s: Int, var cost: Int) : Comparable<Pair?> {
override operator fun compareTo(other: Pair?): Int {
return cost - other!!.cost
}
}
private fun shortestPath(s: Int, d: Int): Int {
val q = PriorityQueue<Pair>()
q.add(Pair(s, 0))
val vis = BooleanArray(n)
while (q.isNotEmpty()) {
val rem = q.remove()
vis[rem.s] = true
if (rem.s == d) return rem.cost
for (e in g[rem.s]!!) {
if (!vis[e.d]) {
q.add(Pair(e.d, rem.cost + e.wt))
}
}
}
return -1
}
}