CodeForces 1741D Masha and a Beautiful Tree
Masha and a Beautiful Tree 经典的分治问题，记录区间的左右端点和区间范围即可。找到一个分支无解之后，及时退出。 // Date: Fri Dec 22 22:12:35 2023 #include <climits> #include <cmath> #include <cstdio> #include <cstdlib> #include <cstring> #include <algorithm> #include <functional> #include <iomanip> #include <iostream> #include <map> #include <queue> #include <set> #include <sstream> #include <stack> #include <string> #include <utility> #include <vector> using namespace std; const int INF = 0x3f3f3f3f, MOD = 1e9 + 7; const double eps = 1e-8; const int dir[8][2] = { {0, 1}, {0, -1}, {1, 0}, {-1, 0}, {1, 1}, {1, -1}, {-1, 1}, {-1, -1}, }; typedef long long ll; typedef unsigned long long ull; typedef vector<int> VI; typedef pair<int, int> PII; const ull Pr = 131; #define For(i, a, b) for (int i = int(a); i < int(b); ++i) #define Rof(i, a, b) for (int i = int(b) - 1; i >= int(a); --i) #define For1(i, a, b) for (int i = int(a); i <= int(b); ++i) #define Rof1(i, a, b) for (int i = int(b); i >= int(a); --i) #define ForE(i, j) for (int i = h[j]; i != -1; i = ne[i]) #define f1 first #define f2 second #define pb push_back #define has(a, x) (a.find(x) != a.end()) #define nonempty(a) (!a.empty()) #define all(a) (a).begin(), (a).end() #define SZ(a) int((a).size()) template <typename t> istream &operator>>(istream &in, vector<t> &vec) { for (t &x : vec) in >> x; return in; } template <typename t> ostream &operator<<(ostream &out, vector<t> &vec) { int n = SZ(vec); For(i, 0, n) { out << vec[i]; if (i < n - 1) out << ' '; } return out; } #ifdef _DEBUG #define debug1(x) cout << #x " = " << x << endl; #define debug2(x, y) cout << #x " = " << x << " " #y " = " << y << endl; #define debug3(x, y, z) \ cout << #x " = " << x << " " #y " = " << y << " " #z " = " << z << endl; #else #define debug1 #define debug2 #define debug3 #endif const int N = 300010; int t, n, a[N]; ll res; void dfs(int l, int r, int vl, int vr) { if (l >= r) return; if (res == -1) return; if (l + 1 == r) { if (a[l] > a[r]) { res++; swap(a[l], a[r]); } if (PII{vl, vr} != PII{a[l], a[r]}) { res = -1; } return; } int mid = (l + r) / 2, vmid = (vl + vr) / 2; if (a[l] >= vl && a[l] <= vmid) { dfs(l, mid, vl, vmid); dfs(mid + 1, r, vmid + 1, vr); } else { res++; dfs(l, mid, vmid + 1, vr); dfs(mid + 1, r, vl, vmid); } } int main(void) { #ifdef _DEBUG freopen("1741d.in", "r", stdin); #endif std::ios::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL); cin >> t; while (t--) { cin >> n; For1(i, 1, n) cin >> a[i]; res = 0; dfs(1, n, 1, n); cout << res << '\n'; } return 0; }