题目描述

Solution

#include <bits/stdc++.h>
using namespace std;
#define js ios::sync_with_stdio(false);cin.tie(0); cout.tie(0)
#define all(__vv__) (__vv__).begin(), (__vv__).end()
#define endl "\n"
#define pai pair<int, int>
#define ms(__x__,__val__) memset(__x__, __val__, sizeof(__x__))
typedef long long ll; typedef unsigned long long ull; typedef long double ld;
inline ll read() { ll s = 0, w = 1; char ch = getchar(); for (; !isdigit(ch); ch = getchar()) if (ch == '-') w = -1; for (; isdigit(ch); ch = getchar())    s = (s << 1) + (s << 3) + (ch ^ 48); return s * w; }
inline void print(ll x, int op = 10) { if (!x) { putchar('0'); if (op)    putchar(op); return; }    char F[40]; ll tmp = x > 0 ? x : -x;    if (x < 0)putchar('-');    int cnt = 0;    while (tmp > 0) { F[cnt++] = tmp % 10 + '0';        tmp /= 10; }    while (cnt > 0)putchar(F[--cnt]);    if (op)    putchar(op); }
inline ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
ll qpow(ll a, ll b) { ll ans = 1;    while (b) { if (b & 1)    ans *= a;        b >>= 1;        a *= a; }    return ans; }    ll qpow(ll a, ll b, ll mod) { ll ans = 1; while (b) { if (b & 1)(ans *= a) %= mod; b >>= 1; (a *= a) %= mod; }return ans % mod; }
const int dir[][2] = { {0,1},{1,0},{0,-1},{-1,0},{1,1},{1,-1},{-1,1},{-1,-1} };
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
const int N = 2e5 + 7;

int n, m, ans;
int dep[N];
vector<int> edge[N];

void dfs(int u, int fa, int cnt) {
    bool flag = 0;
    dep[u] = cnt + 1;
    for (auto& v : edge[u]) {
        if (v == fa)    continue;
        dfs(v, u, cnt + 1);
        if (dep[v] > 2) {
            flag = 1;
            dep[u] = 1;
            dep[v] = 2;
            dep[fa] = 2; // !!!!注意这个
        }
    }
    if (flag)    ++ans;
}

void solve() {
    n = read();
    for (int i = 1; i < n; ++i) {
        int u = read(), v = read();
        edge[u].push_back(v);
        edge[v].push_back(u);
    }
    dfs(1, 0, -1);
    print(ans);
}

int main() {
    int T = 1;
    //T = read();
    while (T--) {
        solve();
    }
    return 0;
}