For problem statement at 1000-1999/1200-1299/1250-1259/1252/problemL.txt this is a correct solution, but verifier at 1000-1999/1200-1299/1250-1259/1252/verifierL.go ends with all tests passed can you fix the verifier? package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
)

type Edge struct {
	to  int
	rev int
	cap int
}

type Dinic struct {
	g     [][]Edge
	level []int
	it    []int
}

func NewDinic(n int) *Dinic {
	return &Dinic{
		g:     make([][]Edge, n),
		level: make([]int, n),
		it:    make([]int, n),
	}
}

func (d *Dinic) AddEdge(fr, to, cap int) int {
	idx := len(d.g[fr])
	d.g[fr] = append(d.g[fr], Edge{to: to, rev: len(d.g[to]), cap: cap})
	d.g[to] = append(d.g[to], Edge{to: fr, rev: idx, cap: 0})
	return idx
}

func (d *Dinic) bfs(s, t int) bool {
	for i := range d.level {
		d.level[i] = -1
	}
	q := make([]int, 1, len(d.g))
	q[0] = s
	d.level[s] = 0
	for head := 0; head < len(q); head++ {
		v := q[head]
		for _, e := range d.g[v] {
			if e.cap > 0 && d.level[e.to] < 0 {
				d.level[e.to] = d.level[v] + 1
				q = append(q, e.to)
			}
		}
	}
	return d.level[t] >= 0
}

func min(a, b int) int {
	if a < b {
		return a
	}
	return b
}

func (d *Dinic) dfs(v, t, f int) int {
	if v == t {
		return f
	}
	for ; d.it[v] < len(d.g[v]); d.it[v]++ {
		i := d.it[v]
		e := &d.g[v][i]
		if e.cap > 0 && d.level[v] < d.level[e.to] {
			ret := d.dfs(e.to, t, min(f, e.cap))
			if ret > 0 {
				e.cap -= ret
				d.g[e.to][e.rev].cap += ret
				return ret
			}
		}
	}
	return 0
}

func (d *Dinic) MaxFlow(s, t int) int {
	const inf = int(1 << 30)
	flow := 0
	for d.bfs(s, t) {
		for i := range d.it {
			d.it[i] = 0
		}
		for {
			f := d.dfs(s, t, inf)
			if f == 0 {
				break
			}
			flow += f
		}
	}
	return flow
}

func main() {
	out := bufio.NewWriterSize(os.Stdout, 1<<20)
	defer out.Flush()

	data, _ := io.ReadAll(os.Stdin)
	idx := 0
	nextInt := func() int {
		for idx < len(data) && (data[idx] < '0' || data[idx] > '9') {
			idx++
		}
		n := 0
		for idx < len(data) && data[idx] >= '0' && data[idx] <= '9' {
			n = n*10 + int(data[idx]-'0')
			idx++
		}
		return n
	}

	N := nextInt()
	K := nextInt()

	U := make([]int, N)
	V := make([]int, N)
	edgeMats := make([][]int, N)
	for i := 0; i < N; i++ {
		a := nextInt() - 1
		m := nextInt()
		U[i] = i
		V[i] = a
		mats := make([]int, m)
		for j := 0; j < m; j++ {
			mats[j] = nextInt()
		}
		edgeMats[i] = mats
	}

	workersByMat := make(map[int][]int, K*2)
	for i := 0; i < K; i++ {
		c := nextInt()
		workersByMat[c] = append(workersByMat[c], i)
	}

	g := make([][]int, N)
	for e := 0; e < N; e++ {
		u, v := U[e], V[e]
		g[u] = append(g[u], e)
		g[v] = append(g[v], e)
	}

	inCycle := make([]bool, N)
	deg := make([]int, N)
	q := make([]int, 0, N)
	for i := 0; i < N; i++ {
		inCycle[i] = true
		deg[i] = len(g[i])
		if deg[i] == 1 {
			q = append(q, i)
		}
	}
	for head := 0; head < len(q); head++ {
		x := q[head]
		if !inCycle[x] {
			continue
		}
		inCycle[x] = false
		for _, e := range g[x] {
			y := U[e] + V[e] - x
			if inCycle[y] {
				deg[y]--
				if deg[y] == 1 {
					q = append(q, y)
				}
			}
		}
	}

	mandatory := make([]bool, N)
	optional := make([]bool, N)
	mandatoryCount := 0
	for e := 0; e < N; e++ {
		if inCycle[U[e]] && inCycle[V[e]] {
			optional[e] = true
		} else {
			mandatory[e] = true
			mandatoryCount++
		}
	}

	matID := make(map[int]int, len(workersByMat))
	materials := make([]int, 0, len(workersByMat))
	for m := range workersByMat {
		matID[m] = len(materials)
		materials = append(materials, m)
	}
	D := len(materials)
	workersListByID := make([][]int, D)
	for id, m := range materials {
		workersListByID[id] = workersByMat[m]
	}

	s := 0
	edgeBase := 1
	matBase := edgeBase + N
	t := matBase + D
	dinic := NewDinic(t + 1)

	sourcePos := make([]int, N)
	for e := 0; e < N; e++ {
		cap := 0
		if mandatory[e] {
			cap = 1
		}
		sourcePos[e] = dinic.AddEdge(s, edgeBase+e, cap)
	}

	for e := 0; e < N; e++ {
		for _, m := range edgeMats[e] {
			if id, ok := matID[m]; ok {
				dinic.AddEdge(edgeBase+e, matBase+id, 1)
			}
		}
	}

	for id := 0; id < D; id++ {
		dinic.AddEdge(matBase+id, t, len(workersListByID[id]))
	}

	flow := dinic.MaxFlow(s, t)
	if flow < mandatoryCount {
		fmt.Fprintln(out, -1)
		return
	}

	for e := 0; e < N; e++ {
		if optional[e] {
			dinic.g[s][sourcePos[e]].cap = 1
		}
	}

	flow += dinic.MaxFlow(s, t)
	if flow < N-1 {
		fmt.Fprintln(out, -1)
		return
	}

	ansU := make([]int, K)
	ansV := make([]int, K)
	nextWorker := make([]int, D)

	for e := 0; e < N; e++ {
		edgeNode := edgeBase + e
		rev := dinic.g[s][sourcePos[e]].rev
		if dinic.g[edgeNode][rev].cap == 0 {
			continue
		}
		matAssigned := -1
		for _, ed := range dinic.g[edgeNode] {
			if ed.to >= matBase && ed.to < t && dinic.g[ed.to][ed.rev].cap > 0 {
				matAssigned = ed.to - matBase
				break
			}
		}
		w := workersListByID[matAssigned][nextWorker[matAssigned]]
		nextWorker[matAssigned]++
		ansU[w] = U[e] + 1
		ansV[w] = V[e] + 1
	}

	for i := 0; i < K; i++ {
		fmt.Fprintf(out, "%d %d\n", ansU[i], ansV[i])
	}
}