[Link] https://www.acmicpc.net/problem/4013
Step 1. get SCC
Step 2.
Method 1
Tarjan is DFS SCC => update dp from biggest idx to lower
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for(int i = groupIdx - 1; i >= 0; i--) {
for(int ge : sccEdges[i]) {
dp[ge] = Math.max(dp[ge], dp[i] + money[ge]);
}
}
Method 2
SCC => DAG(Directed Acyclic Graph) => update dp in order of Topological sort
Method 3
Similar to Method 2, use Dijkstra
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import java.util.*;
import java.io.*;
public class Main {
static BufferedReader br;
// static StringBuilder sb = new StringBuilder();
static ArrayList<Integer>[] edges;
static int[] parent, group;
static boolean[] finish;
static int sccIdx = 1, groupIdx = 0;
static Stack<Integer> stack = new Stack<>();
public static void main(String[] args) throws IOException {
br = new BufferedReader(new InputStreamReader(System.in));
StringBuilder sb = new StringBuilder();
int[] arr = getArr();
int n = arr[0], m = arr[1];
edges = new ArrayList[n];
parent = new int[n];
finish = new boolean[n];
group = new int[n];
Arrays.fill(group, -1);
for(int i = 0; i < n; i++) edges[i] = new ArrayList<>();
for(int i = 0; i < m; i++) {
arr = getArr();
int a = arr[0] - 1, b = arr[1] - 1;
edges[a].add(b);
}
int[] moneyTmp = new int[n];
for(int i = 0; i < n; i++) moneyTmp[i] = toi(br.readLine());
arr = getArr();
int s = arr[0] - 1, p = arr[1];
scc(s);
ArrayList<Integer>[] sccEdges = new ArrayList[sccIdx];
for(int i = 0; i < groupIdx; i++) sccEdges[i] = new ArrayList<>();
boolean[] restaurant = new boolean[groupIdx];
long[] dp = new long[groupIdx];
long[] money = new long[groupIdx];
arr = getArr();
for(int e: arr) {
if(group[e - 1] == -1) continue;
restaurant[group[e - 1]] = true;
}
for(int i = 0; i < n; i++) {
if(group[i] == -1) continue;
money[group[i]] += moneyTmp[i];
for(int e: edges[i]) {
if(group[e] == group[i]) continue;
sccEdges[group[i]].add(group[e]);
}
}
for(int i = 0; i < groupIdx; i++) dp[i] = money[i];
long max = 0;
for(int i = groupIdx - 1; i >= 0; i--) {
for(int ge : sccEdges[i]) {
dp[ge] = Math.max(dp[ge], dp[i] + money[ge]);
}
}
for(int i = 0; i < groupIdx; i++) if(restaurant[i]) max = Math.max(max, dp[i]);
print(max);
}
static int scc(int idx) {
int origVal = parent[idx] = sccIdx++;
stack.push(idx);
for(int e : edges[idx]) {
if(parent[e] == 0) parent[idx] = Math.min(parent[idx], scc(e));
else if(!finish[e]) parent[idx] = Math.min(parent[idx], parent[e]);
}
if(origVal == parent[idx]) {
long totalMoney = 0;
while(true) {
int pop = stack.pop();
finish[pop] = true;
group[pop] = groupIdx;
if(pop == idx) break;
}
groupIdx++;
}
return parent[idx];
}
static int toi(String s) { return Integer.parseInt(s); }
static long tol(String s) { return Long.parseLong(s); }
static String[] getLine() throws IOException { return br.readLine().split(" "); }
static int[] getArr() throws IOException { return Arrays.stream(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray(); }
static <T> void print(T s) { System.out.print(s); }
static <T> void println(T s) { System.out.println(s); }
}