graph new question added

Author: arorarahul

README.md

@@ -185,7 +185,8 @@ it gets converted to i-1,j-1 or we take min or max of i,j-1 and i-1,j
 
 ## Graphs
 
-- Most of the graph questions revolves around finding the adjacent nodes and doing operations on it. Finding adjacent nodes is easy as you can get it from the matrix easily by seeing if the value corresponding to that vertex and some i is 1 and that it has to be unvisited. So basically we either do DFS or BFS
+- Most of the graph questions revolves around finding the adjacent nodes and doing operations on it. Finding adjacent nodes is easy as you can get it from the matrix easily by seeing if the value corresponding to that vertex and some i is 1 and that it has to be unvisited. So basically we either do DFS or BFS.
+- When path between two vertices is to be found, they need not be connected directly
 
 ## Advanced algos
 
@@ -425,6 +426,7 @@ it gets converted to i-1,j-1 or we take min or max of i,j-1 and i-1,j
 - [Implement a graph using adjacency matrix and list, implement DFS and BFS, BST and DST](/graphs/question1.c)
 - [Implement a graph using adjacency matrix and do BFT in a different way for custom value of nodes](/graphs/question2.c)
 - [Write a program to do topological sort in a graph](/graphs/question3.c)
+- [Find if there is a path between two vertices Vi and Vj in a directed graph](/graphs/question4.c)
 
 
 ### Pattern Matching

graphs/question4.c

@@ -0,0 +1,155 @@
+/*
+Find if there is a path between two vertices Vi and Vj in a directed graph
+
+Here path means, they there may or may not be some other vertices as well in the path.
+
+METHOD:
+We can use DFS or BFS and basically if the graph is connected containing these two vertices, if you
+start from one, you will definately get the other one.
+
+Time complexity: O(V+E);
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#define MAX 100
+
+int queue[MAX];
+int rear = -1, front = 0;
+
+int queueElementCount = 0;
+
+int visited[MAX];
+
+struct AdjListNode{
+	int data;
+	struct AdjListNode *next;
+};
+
+struct AdjList{
+	struct AdjListNode *head;
+};
+
+struct Graph{
+	int vertices, edges;
+	struct AdjList *map;
+} *newGraph;
+
+int dequeue(){
+	queueElementCount--;
+	return queue[front++];
+}
+
+void enqueue(int data){
+	queueElementCount++;
+	queue[++rear] = data;
+}
+
+bool isQueueEmpty(){
+	return queueElementCount == 0;
+}
+
+struct AdjListNode *createNode(int data){
+	struct AdjListNode *temp = (struct AdjListNode *)malloc(sizeof(struct AdjListNode));
+	temp->data = data;
+	temp->next = NULL;
+	return temp;
+}
+
+void addEdge(int start, int end){
+	struct AdjListNode *newNode = createNode(end);
+	if(newGraph->map[start].head){
+		newNode->next = newGraph->map[start].head;
+		newGraph->map[start].head = newNode;
+	}else{
+		newGraph->map[start].head = newNode;
+	}
+}
+
+void displayAdjList(){
+	int i;
+
+	for(i=0;i<newGraph->vertices;i++){
+		struct AdjListNode *temp = newGraph->map[i].head;
+		printf("%d --> ", i);
+		while(temp){
+			printf("%d --> ", temp->data);
+			temp = temp->next;
+		}
+		printf("\n");
+	}
+}
+
+int checkDirectlyIfConnected(int v1, int v2){
+	struct AdjListNode *temp = newGraph->map[v1].head;
+
+	while(temp){
+		if(temp->data == v2){
+			return 1;
+		}
+		temp = temp->next;
+	}
+	return 0;
+}
+
+int breadthFirstSearch(int v1, int v2){
+
+	if(checkDirectlyIfConnected(v1, v2)){
+		return 1;
+	}
+
+	visited[v1] = 1;
+	enqueue(v1);
+
+	while(!isQueueEmpty()){
+		int tempVertex = dequeue();
+
+		struct AdjListNode *temp = newGraph->map[tempVertex].head;
+
+		while(temp){
+			if(temp->data == v2){
+				return 1;
+			}else{
+				enqueue(temp->data);
+				visited[temp->data] = 1;
+			}
+			temp = temp->next;
+		}
+
+	}
+
+	return 0;
+
+}
+
+int main(){
+
+	int vertices = 6;
+
+	newGraph = (struct Graph *)malloc(sizeof(struct Graph));
+	newGraph->vertices = vertices;
+	newGraph->map = (struct AdjList *)calloc(sizeof(struct AdjList),vertices);
+
+	addEdge(0,2);
+	addEdge(2,3);
+	addEdge(3,4);
+	addEdge(0,1);
+	addEdge(5,1);
+
+	displayAdjList();
+
+	printf("basis the graph check enter two vertices to see if they are connected or not\n");
+	int v1, v2;
+	scanf("%d %d", &v1, &v2);
+
+	int isConnected = breadthFirstSearch(v1,v2);
+	if(isConnected){
+		printf("YES they are connected\n");
+	}else{
+		printf("NO they are not connected\n");
+	}
+
+	return 0;
+}
+

misc/question2.c

@@ -0,0 +1,75 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+int hash[256];
+
+int cal(char *str){
+
+	int k;
+	for(k=0;k<256;k++){
+		hash[k] = 0;
+	}
+
+	int length = strlen(str);
+
+	int allEqual = true;
+
+	int mid = length/2;
+
+	int max = 0;
+
+	int i = 0;
+	int j = mid;
+
+	int count = 0;
+
+	while(i<mid && j<length){
+
+		if(str[i] == str[j]){
+			i++;
+			j++;
+			count++;
+			if(max < count){
+				max = count;
+			}
+		}else{
+			if(i == 0){
+				j++;
+			}
+			i = 0;
+			count = 0;
+			max = 0;
+		}
+	}
+
+	int z;
+
+	for(z=0;z<length;z++){
+		hash[str[z]]++;
+	}
+
+	if(hash[str[0]] == length){
+		return length-1;
+	}
+
+	return max;
+}
+
+int main(){
+	int cases;
+	scanf("%d", &cases);
+
+	int i;
+
+	char str[100000];
+
+	for(i=0;i<cases;i++){
+		scanf("%s",str);
+		int ans = cal(str);	
+		printf("%d\n", ans);
+	}
+
+	return 0;
+}