性能诊断与 OOM：先定位资源，再选择证据工具

import java.util.*;

public class Main {
    static boolean[] reach(List<List<Integer>> graph,int[] roots,int removed) {
        boolean[] seen=new boolean[graph.size()]; ArrayDeque<Integer> queue=new ArrayDeque<>();
        for(int root:roots) if(root!=removed && !seen[root]) { seen[root]=true; queue.add(root); }
        while(!queue.isEmpty()) {
            int node=queue.remove();
            for(int target:graph.get(node)) if(target!=removed && !seen[target]) {
                seen[target]=true; queue.add(target); // 共享子图与环均只展开一次。
            }
        }
        return seen;
    }
    static long retained(long[] sizes,int[][] edges,int[] roots,int object) {
        Objects.requireNonNull(sizes); Objects.requireNonNull(edges); Objects.requireNonNull(roots);
        int n=sizes.length;
        if(object<0 || object>=n) throw new IllegalArgumentException("object");
        List<List<Integer>> graph=new ArrayList<>();
        for(long size:sizes) { if(size<0)throw new IllegalArgumentException("size");graph.add(new ArrayList<>()); }
        for(int[] edge:edges) {
            if(edge==null || edge.length!=2 || edge[0]<0 || edge[0]>=n || edge[1]<0 || edge[1]>=n)
                throw new IllegalArgumentException("edge");
            graph.get(edge[0]).add(edge[1]);
        }
        for(int root:roots) if(root<0 || root>=n) throw new IllegalArgumentException("root");
        boolean[] before=reach(graph,roots,-1), after=reach(graph,roots,object);
        long total=0;
        for(int i=0;i<n;i++) if(before[i] && !after[i])
            total=Math.addExact(total,sizes[i]); // 只累计因本次移除失去可达性的对象。
        return total; // 原来就不可达的对象不会误计入保留大小。
    }
    static void check(boolean ok) { if(!ok)throw new AssertionError(); }
    public static void main(String[] args) {
        long[] sizes={1,2,10,3}; int[][] graph={{0,1},{0,3},{1,2},{3,2}};
        check(retained(sizes,graph,new int[]{0},1)==2);
        check(retained(sizes,graph,new int[]{0},0)==16);
        check(retained(sizes,graph,new int[]{0,2},0)==6);
        check(retained(new long[]{2,3},new int[][]{{0,1},{1,0}},new int[]{0},0)==5);
        check(retained(new long[]{2,3},new int[0][],new int[]{0},1)==0);
        check(retained(new long[]{2},new int[0][],new int[0],0)==0);
        check(retained(new long[]{0},new int[0][],new int[]{0,0},0)==0);
        try { retained(new long[]{Long.MAX_VALUE,1},new int[][]{{0,1}},new int[]{0},0);throw new AssertionError(); }
        catch(ArithmeticException expected) { }
        System.out.println("PASS 8");
    }
}