Create shortest-path-with-alternating-colors.cpp

Author: kamyu104

C++/shortest-path-with-alternating-colors.cpp

@@ -0,0 +1,36 @@
+// Time:  O(n + e), e is the number of red and blue edges
+// Space: O(n + e)
+
+class Solution {
+public:
+    vector<int> shortestAlternatingPaths(int n, vector<vector<int>>& red_edges, vector<vector<int>>& blue_edges) {
+        vector<vector<unordered_set<int>>> neighbors(n, vector<unordered_set<int>>(2));
+        for (const auto& edge : red_edges) {
+            neighbors[edge[0]][0].emplace(edge[1]);
+        }
+        for (const auto& edge : blue_edges) {
+            neighbors[edge[0]][1].emplace(edge[1]);
+        }
+        const auto& INF = max(2 * n - 3, 0) + 1;
+        vector<vector<int>> dist(n, vector<int>(2, INF));
+        dist[0] = {0, 0};
+        queue<pair<int, int>> q({{0, 0}, {0, 1}});
+        while (!q.empty()) {
+            int i, c;
+            tie(i, c) = q.front(); q.pop();
+            for (const auto& j : neighbors[i][c]) {
+                if (dist[j][c] != INF) {
+                    continue;
+                }
+                dist[j][c] = dist[i][1 ^ c] + 1;
+                q.emplace(j, 1 ^ c);
+            }
+        }
+        vector<int> result;
+        for (const auto& d : dist) {
+            const auto& x = *min_element(d.cbegin(), d.cend());
+            result.emplace_back((x != INF) ? x : -1);
+        }
+        return result;
+    }
+};