I think my method is right, but it always gets WR!
Thank u!


#include "stdio.h"

int n, m, M[201][201];
int B[201][2], F[201];

void Init() {
    int i, j, k;

    scanf("%d %d",&n,&m);
    for (i=1; i<=n; i++)
        for (j=1; j<=n; j++) M[i][j] = 0;

    for (k=0; k<m; k++) {
        scanf("%d %d",&i,&j);
        if (i!=j) M[i][j] = M[j][i] = 1;
    }
}

void CT(int num, int father, int level) {
    int i;
    F[num] = 1;
    B[num][0] = father; B[num][1] = level;
    for (i=1; i<=n; i++)
        if (!F[i] && M[num][i]) {
            M[num][i] = M[i][num] = 0;
            CT(i, num, level+1);
        }
}

void CreateTree() {
    int i;

    for (i=1; i<=n; i++) F[i] = 0;

/*    for (i=1; i<=n; i++)
        if (!F[i]) {
            Pth[0] = i; nail = head = 0;
            B[i][0] = 0; B[i][1] = 1; F[i] = 1;
            while (head<=nail) {
                j = Pth[head]; head++;
                for (k=1; k<=n; k++)
                    if (!F[k] && M[j][k]) {
                        nail++; Pth[nail] = k;
                        B[k][0] = j; B[k][1]
= B[j][1] + 1;
                        F[k] = 1;
                        M[j][k] = M[k][j] = 0;
                    }
            }
        }*/
    for (i=1; i<=n; i++) {
        if (!F[i]) CT(i, 0, 1);
    }
/*    for (i=1; i<=n; i++) printf("%d %d\n",B[i][0],B[i][1]);*/
}

void Caculate() {
    int total, i, j;
    int Pth[2][201], l[2];

    for (i=1, total=0; i<=n; i++)
        for (j=1; j<=n; j++)
            if (M[i][j]==1) {
                total++;
                M[i][j] = M[j][i] = 2;
            }
    printf("%d\n",total);

    for (i=1; i<=n; i++)
        for (j=1; j<=n; j++)
            if (M[i][j]==2) {
                M[i][j] = M[j][i] = 0;
                l[0] = l[1] = 0;
                Pth[0][0] = i;
                Pth[1][0] = j;

                while (Pth[0][l[0]]!=Pth[1][l[1]])
                    if (B[Pth[0][l[0]]][1]==B[Pth
[1][l[1]]][1]) {
                        l[0]++; Pth[0][l[0]]
= B[Pth[0][l[0]-1]][0];
                        l[1]++; Pth[1][l[1]]
= B[Pth[1][l[1]-1]][0];
                    }
                    else if (B[Pth[0][l[0]]][1]>B
[Pth[1][l[1]]][1]) {
                        l[0]++; Pth[0][l[0]]
= B[Pth[0][l[0]-1]][0];
                    }
                    else {
                        l[1]++; Pth[1][l[1]]
= B[Pth[1][l[1]-1]][0];
                    }

                printf("%d",l[0]+l[1]+1);
                for (i=0; i<=l[0]; i++) printf(" %
d",Pth[0][i]);
                for (i=l[1]-1; i>=0; i--) printf(" %
d",Pth[1][i]);
                printf("\n");
            }

}

main() {
    Init();
    CreateTree();
    Caculate();
}