class Graph {
    constructor() {
        this.adjacencyList = {};
    }
    addVertex(vertex) {
        if(!this.adjacencyList[vertex]) {
          this.adjacencyList[vertex] = [];  
        }
        return g;
    }

    addEdge(v1,v2) {
        this.adjacencyList[v1].push(v2);
        this.adjacencyList[v2].push(v1);
        return g;
    } 

    removeEdge(vertex1,vertex2) {
        this.adjacencyList[vertex1] = this.adjacencyList[vertex1].filter(
            v => v !== vertex2
        );
        this.adjacencyList[vertex2] = this.adjacencyList[vertex2].filter(
            v => v !== vertex1
        );
        return g;
    } 

    removeVertex(vertex) {
        while (this.adjacencyList[vertex].length) {
            const adjacencyVertex = this.adjacencyList[vertex].pop()
            this.removeEdge(vertex, adjacencyVertex);
        }
        delete this.adjacencyList[vertex]
        return g;
    }

    depthFirstRecursive(start) {
        const result = [];
        const visited = {};
        const adjacencyList = this.adjacencyList;

        (function dfs(vertex) {
            if(!vertex) return null;
            visited[vertex] = true;
            result.push(vertex);
            adjacencyList[vertex].forEach(neighbor => {
                if(!visited[neighbor]) {
                    return dfs(neighbor)
                }
            });
        })(start);
        return result;
    }

    depthFirstIterative(start) {
        const stack = [start];
        const result = [];
        const visited = {};
        let currentVertex;

        visited[start] = true;
        while(stack.length) {
            console.log(stack);
            currentVertex = stack.pop();
            result.push(currentVertex);

            this.adjacencyList[currentVertex].forEach(neighbor => {
                if(!visited[neighbor]) {
                    visited[neighbor] = true;
                    stack.push(neighbor)
                }
            });
        }
        return result;
    }
    breadthFirst(start) {
        const queue = [start];
        const result = [];
        const visited = {};
        let currentVertex;

        while(queue.length) {
             currentVertex = queue.shift()
             result.push(currentVertex);

             this.adjacencyList[currentVertex].forEach(neighbor => {
                if(!visited[neighbor]) {
                    visited[neighbor] = true;
                    queue.push(neighbor)
                }
             });
        }
        return result;
    }
}

let g =new Graph();
g.addVertex("A")
g.addVertex("B")
g.addVertex("C")
g.addVertex("D")
g.addVertex("E")
g.addVertex("F")

g.addEdge("A","B")
g.addEdge("A","C")
g.addEdge("B","D")
g.addEdge("C","E")
g.addEdge("D","E")
g.addEdge("D","F")
g.addEdge("E","F")


/*
             A
           /   \
          B     C
          |     | 
          D --- E
           \   /
             F
*/