Create 2699. Modify Graph Edge Weights (#571)

Author: Chayandas07

2699. Modify Graph Edge Weights

@@ -0,0 +1,74 @@
+class Solution {
+public:
+    vector<vector<int>> modifiedGraphEdges(int n, vector<vector<int>>& edges, int source, int destination, int target) {
+          constexpr int kMax = 2'000'000'000;
+    vector<vector<pair<int, int>>> graph(n);
+
+    for (const vector<int>& edge : edges) {
+      const int u = edge[0];
+      const int v = edge[1];
+      const int w = edge[2];
+      if (w == -1)
+        continue;
+      graph[u].emplace_back(v, w);
+      graph[v].emplace_back(u, w);
+    }
+
+    int distToDestination = dijkstra(graph, source, destination);
+    if (distToDestination < target)
+      return {};
+    if (distToDestination == target) {
+      // Change the weights of negative edges to an impossible value.
+      for (vector<int>& edge : edges)
+        if (edge[2] == -1)
+          edge[2] = kMax;
+      return edges;
+    }
+
+    for (int i = 0; i < edges.size(); ++i) {
+      const int u = edges[i][0];
+      const int v = edges[i][1];
+      int& w = edges[i][2];
+      if (w != -1)
+        continue;
+      w = 1;
+      graph[u].emplace_back(v, 1);
+      graph[v].emplace_back(u, 1);
+      distToDestination = dijkstra(graph, source, destination);
+      if (distToDestination <= target) {
+        w += target - distToDestination;
+        // Change the weights of negative edges to an impossible value.
+        for (int j = i + 1; j < edges.size(); ++j)
+          if (edges[j][2] == -1)
+            edges[j][2] = kMax;
+        return edges;
+      }
+    }
+
+    return {};
+  }
+
+ private:
+  int dijkstra(const vector<vector<pair<int, int>>>& graph, int src, int dst) {
+    vector<int> dist(graph.size(), INT_MAX);
+    using P = pair<int, int>;  // (d, u)
+    priority_queue<P, vector<P>, greater<>> minHeap;
+
+    dist[src] = 0;
+    minHeap.emplace(dist[src], src);
+
+    while (!minHeap.empty()) {
+      const auto [d, u] = minHeap.top();
+      minHeap.pop();
+      if (d > dist[u])
+        continue;
+      for (const auto& [v, w] : graph[u])
+        if (d + w < dist[v]) {
+          dist[v] = d + w;
+          minHeap.emplace(dist[v], v);
+        }
+    }
+
+    return dist[dst]; 
+    }
+};