684 685

Author: LuYanFCP

cpp/684.cpp

@@ -0,0 +1,32 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+public:
+    vector<int> findRedundantConnection(vector<vector<int>>& edges) {
+        vector<int> res{0, 0};
+        init_uf(2*edges.size());
+        for (vector<int>& edge:edges) {
+            int first_root = find_uf(edge[0]);
+            int second_root = find_uf(edge[1]);
+            if (first_root == second_root) {
+                res = edge; // copy assign
+                continue;
+            }
+            parents[first_root] = second_root;
+        }
+        return res;
+    }
+    void init_uf(size_t n) {
+        auto it = back_insert_iterator(parents);
+        for (int i=0; i < n; ++i) it++ = i;
+    }
+    int find_uf(int x) {
+        int i;
+        for (i = x; i != parents[i]; i=parents[i]);
+        return i;
+    }
+
+private:
+    vector<int> parents;
+};

cpp/685.cpp

@@ -0,0 +1,72 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+public:
+    vector<int> findRedundantDirectedConnection(vector<vector<int>>& edges) {
+        /* 进行统计 */
+        int E = edges.size();
+        vector<int> counter(2*E, 0);
+        vector<vector<int>> idxs(2*E, vector<int>());  // 记录边的位置
+        int target_node = -1;  // 找两个入度的node
+        for (int i = 0; i < E; ++i) {
+            auto edge = edges[i];
+            counter[edge[1]]++;
+            idxs[edge[1]].push_back(i);
+            if (counter[edge[1]] == 2) {
+                target_node = edge[1];
+                break;
+            }
+        }
+        // 判断, 是不是是环
+        if (target_node == -1) {
+
+            init_uf(2*E);
+            for (int i = 0; i < E; ++i) {
+                auto edge = edges[i];
+                int first_root = find_uf(edge[0]);
+                int second_root = find_uf(edge[1]);
+                if (first_root == second_root) {
+                    return edge;  // 找到了环路的最后一个
+                }
+                parents[first_root] = second_root;
+            }
+        }
+        // printf("%d==%d,%d\n", target_node, idxs[target_node][0], idxs[target_node][1]);
+        // 如果不是环
+        vector<int> res;
+        for (int idx: idxs[target_node]) {
+            init_uf(2*E);
+            int i = 0;
+            for (i = 0; i < E; ++i) {
+                if (i==idx) continue;
+                auto edge = edges[i];
+                int first_root = find_uf(edge[0]);
+                int second_root = find_uf(edge[1]);
+                if (first_root == second_root) {
+                    // 不是树
+                    break;
+                }
+                parents[first_root] = second_root;
+            }
+            if (i == E) {
+                res = edges[idx];
+            }
+        }
+        return res;
+
+    }
+    void init_uf(size_t n) {
+        parents.clear();
+        auto it = back_insert_iterator(parents);
+        for (int i=0; i < n; ++i) it++ = i;
+    }
+    int find_uf(int x) {
+        int i;
+        for (i = x; i != parents[i]; i=parents[i]);
+        return i;
+    }
+
+private:
+    vector<int> parents;
+};