- Translate each rule into one explicit state update.
- Maintain the invariant after every processed item.
- Return the accumulated state once all relevant input has been handled.
Code notes
- 67 lines of C++ from the credited upstream file abc075_c.cpp.
- The implementation visibly relies on sequence storage, ordered lookup.
- 3 loop blocks detected.
Complexity
Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.
Check the problem constraints before deciding whether this complexity will pass.
Use this to learn the idea, then write your own version.
1#include <iostream>2#include <map>3#include <vector>4 5using namespace std;6 7bool traverse(map<int, vector<int>> edges, int prev_vertex, int current_vertex,8 map<int, bool> root, vector<int> root_vec) {9 bool loop = false;10 for (auto& e : edges[current_vertex]) {11 if (e == prev_vertex) {12 continue;13 }14 if (e == root_vec[0]) {15 return true;16 }17 if (root.count(e) != 0) {18 continue;19 }20 root[e] = true;21 root_vec.push_back(e);22 loop = loop || traverse(edges, current_vertex, e, root, root_vec);23 }24 25 return loop;26}27 28int main() {29 int n, m;30 cin >> n >> m;31 32 if (n - 1 == m) {33 cout << m << endl;34 return 0;35 }36 37 map<int, vector<int>> edges;38 map<int, bool> vertices;39 for (int i = 0; i < m; i++) {40 int a, b;41 cin >> a >> b;42 if (edges.count(a) == 0) {43 edges[a] = {b};44 } else {45 edges[a].push_back(b);46 }47 if (edges.count(b) == 0) {48 edges[b] = {a};49 } else {50 edges[b].push_back(a);51 }52 53 vertices[a] = true;54 vertices[b] = true;55 }56 57 int loop_gen_vertices_count = 0;58 auto v_iter = vertices.begin();59 while (v_iter != vertices.end()) {60 bool is_loop = traverse(edges, 0, v_iter->first,61 {{v_iter->first, true}}, {v_iter->first});62 loop_gen_vertices_count += int(is_loop);63 v_iter++;64 }65 66 cout << n - loop_gen_vertices_count << endl;67}