Problem p02776 (python)

Fixed submission:
import bisect
import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**6)


def dfs(v, x, g, used, ans):
    used[v] = True
    res = x[v]
    for e in g[v]:
        if used[e[0]]:
            continue
        r = dfs(e[0], x, g, used, ans)
        if r:
            ans.append(e[1])
        res ^= r
    return res


def main():
    n, m = map(int, input().split())
    ab = [[] for _ in range(n)]
    ans = []
    g = [[] for _ in range(n+1)]
    used = [False] * (n+1)

    for i in range(n):
        ab[i] = list(map(int, input().split()))
    ab = sorted(ab, key=lambda x: x[0])
    al = list(map(lambda x: x[0], ab))
    for i in range(m):
        l, r = map(int, input().split())
        l = bisect.bisect_left(al, l)
        r = bisect.bisect_right(al, r)
        g[l].append((r, i+1))
        g[r].append((l, i+1))

    x = [0] * (n+1)
    x[0] = ab[0][1]
    for i in range(n-1):
        x[i+1] = ab[i][1] ^ ab[i+1][1]
    x[n] = ab[n-1][1]

    for i in range(n+1):
        if used[i]:
            continue
        if dfs(i, x, g, used, ans):
            print(-1)
            return

    ans.sort()
    print(len(ans))
    print(*ans)


main()

Buggy submission (verdict: Runtime Error):
import bisect


def dfs(v, x, g, used, ans):
    used[v] = True
    res = x[v]
    for e in g[v]:
        if used[e[0]]:
            continue
        r = dfs(e[0], x, g, used, ans)
        if r:
            ans.append(e[1])
        res ^= r
    return res


def main():
    n, m = map(int, input().split())
    ab = [[] for _ in range(n)]
    ans = []
    g = [[] for _ in range(n+1)]
    used = [False] * (n+1)

    for i in range(n):
        ab[i] = list(map(int, input().split()))
    ab = sorted(ab, key=lambda x: x[0])
    al = list(map(lambda x: x[0], ab))
    for i in range(m):
        l, r = map(int, input().split())
        l = bisect.bisect_left(al, l)
        r = bisect.bisect_right(al, r)
        g[l].append((r, i+1))
        g[r].append((l, i+1))

    x = [0] * (n+1)
    x[0] = ab[0][1]
    for i in range(n-1):
        x[i+1] = ab[i][1] ^ ab[i+1][1]
    x[n] = ab[n-1][1]

    for i in range(n+1):
        if used[i]:
            continue
        if dfs(i, x, g, used, ans):
            print(-1)
            return

    ans.sort()
    print(len(ans))
    print(*ans)


main()

Buggy submission (verdict: Runtime Error):
import bisect


def dfs(v, x, g, used, ans):
    used[v] = True
    res = x[v]
    for e in g[v]:
        if used[e[0]]:
            continue
        r = dfs(e[0], x, g, used, ans)
        if r:
            ans.append(e[1])
        res ^= r
    return res


def main():
    n, m = map(int, input().split())
    ab = []
    ans = []
    g = [[] for _ in range(n+1)]
    used = [False] * (n+1)

    for i in range(n):
        ab.append(list(map(int, input().split())))
    ab = sorted(ab, key=lambda x: x[0])
    al = list(map(lambda x: x[0], ab))
    for i in range(m):
        l, r = map(int, input().split())
        l = bisect.bisect_left(al, l)
        r = bisect.bisect_right(al, r)
        g[l].append((r, i+1))
        g[r].append((l, i+1))

    x = [ab[0][1]]
    for i in range(n-1):
        x.append(ab[i][1] ^ ab[i+1][1])
    x.append(ab[n-1][1])

    for i in range(n+1):
        if used[i]:
            continue
        if dfs(i, x, g, used, ans):
            print(-1)
            return

    ans.sort()
    print(len(ans))
    print(*ans)


main()