Codeforces 337D D. Book of Evil (tree DP)

Topic Links:

Codeforces 337D

Main topic:

Give a tree, give the infection range, give some identified the infected point, ask the number of points the infection may be placed.

Topic Analysis:

• Define state Dp[i] represents the distance at which a point reaches the identified point of infection farthest from it.
• Then we first DFS again, the tree with 1 roots, each point to the maximum distance of the infection point in the subtree, and then DFS again, to obtain dp[i] the required value, using a dd[i] array to represent the father of point I, in addition to their own and the root of the sub-tree point of infection point to their farthest distance.
• Then processing out each point son's prefix and suffix of the maximum value, and then use DD can be obtained dp[i], the specific transfer process see code, relatively simple, unclear local comment area ...
  

AC Code:

#include <iostream># include <cstring>#include <cstdio>#include <algorithm>#include <vector>#define MAX 100007#define INF (-(1<<29));using namespace STD;intN,m,d;intDp[max];intDd[max];intMark[max];intLef[max],rig[max]; vector<int>E[max];voidAdd (intU,intV) {e[u].push_back (v); E[v].push_back (u);}voidDFS (intU,intP) {if(Mark[u]) dp[u] =0;ElseDp[u] = INF; for(inti =0; I < e[u].size (); i++) {intv = e[u][i];if(v = = p)Continue;        DFS (v, u); Dp[u] = max (Dp[u], Dp[v] +1); }}voidDFS1 (intU,intP) {lef[0] = INF; Rig[e[u].size () +1] = INF; for(inti =0; I < e[u].size (); i++) {intx = i+1;intv = e[u][i];if(v = = p) {Lef[x] = lef[x-1];Continue; } Lef[x] = max (lef[x-1], dp[v]); } for(inti = e[u].size ()-1; I >=0; i--) {intx = i+1;intv = e[u][i];if(v = = p) {Rig[x] = rig[x+1];Continue; } Rig[x] = max (rig[x+1], dp[v]); } for(inti =0; I < e[u].size (); i++) {intv = e[u][i];if(v = = p)Continue; DD[V] = max (Dd[u], Max (lef[i), rig[i+2])+1)+1;    DP[V] = max (Dp[v], dd[v]); } for(inti =0; I < e[u].size (); i++) {intv = e[u][i];if(v = = p)Continue;    DFS1 (V, u); }   }voidClear () { for(inti =0; i < MAX; i++) E[i].clear ();}intMain () { while( ~scanf("%d%d%d", &n, &m, &d)) {intx, y; Clear ();memset(Mark,0,sizeof(Mark));memset(DD,-0x3f,sizeof(DD)); for(inti =0; I < m; i++) {scanf("%d", &x); MARK[X] =1; } for(inti =1; I < n; i++) {scanf("%d%d", &x, &y);        Add (x, y); } DFS (1, -1);if(mark[1]) dd[1] =0;Elsedd[1] = INF; DFS1 (1, -1);intAns =0; for(inti =1; I <= N; i + +)if(Dp[i] <= d && Dp[i] >=0) ans++;printf("%d\n", ans); }}

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Codeforces 337D D. Book of Evil (tree DP)