CF 1029E Tree with Small Distances

#include <cstdio>
#include <cstring>
using namespace std;

const int N = 2e5 + 5;

int n, ans = 0, tot = 0, head[N];

struct Edge {
    int to, nxt;
} e[N << 1];

inline void add(int from, int to) {
    e[++tot].to = to;
    e[tot].nxt = head[from];
    head[from] = tot;
}

inline void read(int &X) {
    X = 0;
    char ch = 0;
    int op = 1;
    for(; ch > ‘9‘|| ch < ‘0‘; ch = getchar())
        if(ch == ‘-‘) op = -1;
    for(; ch >= ‘0‘ && ch <= ‘9‘; ch = getchar())
        X = (X << 3) + (X << 1) + ch - 48;
    X *= op;
}

inline void chkMin(int &x, int y) {
    if(y < x) x = y;
}

int dfs(int x, int fat) {
    int dis = 2;
    for(int i = head[x]; i; i = e[i].nxt) {
        int y = e[i].to;
        if(y == fat) continue;
        chkMin(dis, dfs(y, x));
    }
    
    if(dis == 0 && x != 1 && fat != 1) ans++;
    return (dis + 1) % 3;
}

int main() {
    read(n);
    for(int x, y, i = 1; i < n; i++) {
        read(x), read(y);
        add(x, y), add(y, x);
    }
    dfs(1, 0);
    printf("%d\n", ans);
    return 0;
}