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@pankajyd/

Check Bipartite Graph

C

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  • main.c
main.c
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#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>

/************************************
                white = 0
                grey = 1
                black = 2
************************************/


typedef struct vertex{
    int v;
    int d;
    int color;
    struct list_entry* head;
}vertex;

typedef struct list_entry{
    struct vertex* self;
    struct list_entry* next;
}list_entry;

typedef struct Queue{
    int n;
    int* Q;
    int head;
    int tail;
}Queue;

int IsEmpty(Queue* Q){
    if(Q->head == Q->tail)
        return 1;
    return 0;
}

int IsFull(Queue* Q){
    int i = Q->tail;

    if(Q->tail == Q->n - 1)
        i = 0;
    else
        i++;
    
    if(i == Q->head)
        return 1;
    return 0;
}

void Enqueue(Queue* Q, int x){
    if(!IsFull(Q)){
        Q->Q[Q->tail] = x;
    }
    else{
        return;
    }
    if(Q->tail == Q->n - 1){
        Q->tail = 0;
    }
    else{
        Q->tail++;
    }
}

int Dequeue(Queue* Q){
    int x;
    if(!IsEmpty(Q))
        x = Q->Q[Q->head];
    if(Q->head == Q->n - 1)
        Q->head = 1;
    else
        Q->head++;
    return x;
}

int BFS(vertex* V, int i, int nv){
    int q[nv];
    Queue QQ;
    Queue* Q = &QQ;
    Q->n = nv;
    Q->Q = q;
    Q->head = 0;
    Q->tail = 0;

	V[i].d = 0;
	V[i].color = 1;
	Enqueue(Q, i);
	//printf("\nEnqueued %d", i);
	while(!IsEmpty(Q)){
		int u = Dequeue(Q);
		//printf("\nDequeued %d", u);
		list_entry* head = V[u].head;
		//printf("\nTraversing Adjaceny list of vertex %d", u);
		while(head != NULL){
			//printf("\n\t Now at vertex %d", head->self->v);
			if(head->self->color == 0){
				head->self->d = V[u].d + 1;
				head->self->color = 1;
				Enqueue(Q, head->self->v);
				//printf("\nEnqueued %d", i);
			}
			else if(head->self->d == V[u].d){
				//printf("\nBFS exited. Not bipartite.");
				return 0;
			}
			head = head->next;
		}
	}
	return 1;
}


int check_bipartite(vertex* V, int nv){
	for(int i = 1; i < nv; i++){
		//printf("\nStarting BFS with vertex: %d\n", i);
		if(V[i].color == 0){
			if(!BFS(V, i, nv)){
				return 0;
			}
		}
	}
	return 1;
}


int main() {
    int t;
    scanf("%d", &t);
    
    vertex* V;
    
    while(t--){
        int nv, ne;
        scanf("%d %d", &nv, &ne);
        nv++;
        vertex G[nv];
        V = G;
        
        list_entry* v_tail[nv];
        
        //Initializing colors to white and pointers to NULL
        for(int i = 1; i < nv; i++){
            V[i].v = i;
            
            V[i].color = 0;
            
            V[i].head = NULL;
            v_tail[i] = NULL;
        }

        //Scanning Edges
        for(int i = 0; i < ne; i++){
            int v1, v2;
            scanf("%d %d", &v1, &v2);
            
            list_entry* ptr;
            
            ptr = (list_entry*)malloc(sizeof(list_entry));           
            ptr->self = &V[v2];
            ptr->next = NULL;
            
            list_entry* ptr2;
            
            ptr2 = (list_entry*)malloc(sizeof(list_entry));           
            ptr2->self = &V[v1];
            ptr2->next = NULL;

			//Edge u to v
            if(V[v1].head == NULL){
                V[v1].head = ptr;
            }
            else{
                v_tail[v1]->next = ptr;
            }
            v_tail[v1] = ptr;

			//Edge v to u
            if(V[v2].head == NULL){
                V[v2].head = ptr2;
			}
            else{
                v_tail[v2]->next = ptr2;
			}
            v_tail[v2] = ptr2;
        }
        
        if(check_bipartite(V, nv))
            printf("Yes\n");
        else
            printf("No\n");
    }
    return 0;
}