b.cpp

#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define f first
#define s second
#define mp make_pair

using namespace std;
const int MAXN = 1e5 + 100;
const int MOD = 1e9 + 7;

int dp[MAXN], dpH[MAXN];
vector <int> g[MAXN];
bool removed[MAXN];
ll ans;
map <int, int> allDist;

int n, k;

int sizeComp(int x, int pr = -1){
    dp[x] = 1;
    for (int i = 0; i < g[x].size(); i++){
        int to = g[x][i];
        if (to == pr)
            continue;
        if (!removed[to]){
            dp[x] += sizeComp(to, x);
        }
    }

    return dp[x];
}

void findDist(int x, int h = 1, int pr = -1){
    dpH[x] = h;
    ans += allDist[k - dpH[x]];
    for (int i = 0; i < g[x].size(); i++){
        int to = g[x][i];
        if (to == pr)
            continue;
        if (!removed[to]){
            findDist(to, h + 1, x);
        }
    }
}
void addDist(int x, int pr = -1){
    allDist[dpH[x]]++;
    //cout << "x = " << x << ' ' << "dpH[x] = " << dpH[x] << endl;
    for (int i = 0; i < g[x].size(); i++){
        int to = g[x][i];
        if (to == pr)
            continue;
        if (!removed[to]){
            addDist(to, x);
        }
    }
}

int findC(int x, int sz, int pr = -1){

    for (int i = 0; i < g[x].size(); i++){
        int to = g[x][i];
        if (to == pr)
            continue;
        if (!removed[to] && dp[to] * 2 > sz){
            return findC(to, sz, x);
        }
    }

    return x;
}

void calc(int c){

    //cout << "c = " << c << endl;
    for (int i = 0; i < g[c].size(); i++){
        int to = g[c][i];
        if (!removed[to]){
            findDist(to);
            addDist(to);
        }
    }

    ans += allDist[k];
}



void solve(int x, int cnt = 0){
    int sz = sizeComp(x);
    int c = findC(x, sz);

    removed[c] = 1;

    //ans[c] = cnt;
    allDist.clear();
    calc(c);
    for (int i = 0; i < g[c].size(); i++){
        int to = g[c][i];
        if (!removed[to]){

            solve(to, cnt + 1);
        }
    }

}
int main(){
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> n >> k;
    for (int i = 1; i < n; i++){
        int x, y;
        cin >> x >> y;
        g[x].pb(y);
        g[y].pb(x);
    }

    solve(1);
    cout << ans;

}