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Author: MishkatIT

1976-number-of-ways-to-arrive-at-destination/1976-number-of-ways-to-arrive-at-destination.cpp

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+class Solution {
+public:
+    int countPaths(int n, vector<vector<int>>& roads) {
+        const int mod = 1e9 + 7;
+        vector<vector<pair<int, int>>> g(n);
+        
+        for (auto &r : roads) {
+            g[r[0]].push_back({r[1], r[2]});
+            g[r[1]].push_back({r[0], r[2]});
+        }
+        
+        // Min-heap for Dijkstra {time, node}
+        priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<>> pq;
+        vector<long long> dist(n, LLONG_MAX);
+        vector<int> ways(n, 0);
+        
+        dist[0] = 0;
+        ways[0] = 1;
+        pq.push({0, 0});
+        
+        while (!pq.empty()) {
+            auto [curTime, u] = pq.top(); pq.pop();
+            if (curTime > dist[u]) continue; // Ignore outdated entries
+            for (auto &[v, time] : g[u]) {
+                long long newTime = curTime + time;
+                
+                if (newTime < dist[v]) {
+                    dist[v] = newTime;
+                    ways[v] = ways[u];
+                    pq.push({newTime, v});
+                } else if (newTime == dist[v]) {
+                    ways[v] = (ways[v] + ways[u]) % mod;
+                }
+            }
+        }
+        return ways[n-1];
+    }
+};