Codeforces161d-distance in tree-like DP

Question: give you a tree and ask you how many conditions the distance between the trees is K.

Solution: tree-like DP maintains the depth of each node (1-K,

Solution code:

1 // file name: 161d. CPP 2 // Author: darkdream 3 // created time: sunday, September 11, August 03, 2014 4 5 # include <vector> 6 # include <list> 7 # include <map> 8 # include <set> 9 # include <deque> 10 # include <stack> 11 # include <bitset> 12 # include <algorithm> 13 # include <functional> 14 # include <numeric> 15 # include <utility> 16 # include <sstream> 17 # include <iostream> 18 # include <iomanip> 19 # include <cstdio> 20 # include <cmath> 2 1 # include <cstdlib> 22 # include <cstring> 23 # include <ctime> 24 # define ll long long25 26 using namespace STD; 27 28 vector <int> A [50004]; 29 int M [50005] [500]; 30 int visit [50004]; 31 int N, K; 32 ll ans = 0; 33 void DFS (int t) 34 {35 int lT = A [T]. size (); 36 m [T] [0] = 1; 37 for (INT I = 0; I <lt; I ++) 38 {39 int TT = A [T] [I]; 40 if (! Visit [TT]) 41 {42 visit [TT] = 1; 43 DFS (TT); 44 for (Int J = 0; j <K; j ++) 45 ans + = m [T] [k-j-1] * m [TT] [J]; 46 for (Int J = 0; j <K; j ++) 47 {48 m [T] [J + 1] + = m [TT] [J]; 49} 50} 51} 52} 53 int main () {54 scanf ("% d", & N, & K); 55 int Ta, TB; 56 memset (M, 0, sizeof (m )); 57 memset (visit, 0, sizeof (visit); 58 for (INT I = 1; I <= n-1; I ++) 59 {60 scanf ("% d", & TA, & TB); 61 A [Ta]. push_back (TB); 62 A [TB]. push_back (TA); 63} 64 visit [1] = 1; 65 DFS (1); 66 printf ("% i64d \ n", ANS); 67 return 0; 68}

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