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// 1466. Reorder Routes to Make All Paths Lead to the City Zero
#include "leetcode.h"
/*
* there are 'n' cities numbered from 0 to 'n - 1' and 'n - 1'
* roads such that there is only one way to travel between two
* different cities (this network forms a tree). last year, the
* ministry of transport decided to orient the roads in one
* direction because they are too narrow.
* roads are represented by 'connections' where 'connections[i] = [ai, bi]'
* represents a road from city 'ai' to city 'bi'.
* this year, there will be a big event in the capital (city 0),
* and many people will want to travel to the city. task consists
* reorienting some roads such that each city can visit city 0.
* return minimum number of edges changed.
*/
class Solution {
public:
int minReorder(int n, vvd(int) & connections) {
vvd(int) ans(n);
for (auto &c : connections) {
ans[c[0]].push_back(c[1]);
ans[c[1]].push_back(-c[0]);
}
return dfs(ans, vector<bool>(n) = {}, 0);
}
private:
int dfs(vvd(int) & res, vector<bool> visited, int from) {
auto change = 0;
visited[from] = true;
for (auto to : res[from])
if (!visited[abs(to)])
change += dfs(res, visited, abs(to)) + (to > 0);
return change;
}
};
int main() {
Solution obj;
vvd(int) connections1 = {{0, 1}, {1, 3}, {2, 3}, {4, 0}, {4, 5}};
vvd(int) connections2 = {{1, 0}, {1, 2}, {3, 2}, {3, 4}};
vvd(int) connections3 = {{1, 0}, {2, 0}};
cout << obj.minReorder(6, connections1) << endl; // expect: 3
cout << obj.minReorder(5, connections2) << endl; // expect: 2
cout << obj.minReorder(3, connections3) << endl; // expect: 0
}
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