Java Solution with Explanation(DFS)
\n\n# Approach and Explanation\n Describe your approach to solving the problem. \n1. This code is solving the problem of finding the minimum time required to co
\n\n# Approach and Explanation\n<!-- Describe your approach to solving the problem. -->\n1. This code is solving the problem of finding the minimum time required to collect all apples in a given tree. The tree is represented by a list of edges, where each edge connects two nodes, and a list of booleans that indicates whether each node has an apple or not.\n\n2. The main function "minTime" takes in 3 arguments:\n\n- n: number of nodes in the tree\n- edges: a 2D array representing the edges of the tree\n- hasApple: a list of booleans indicating whether each node has an apple or not.\n\nIt starts by creating an adjacency list representation of the tree from the given edges. An adjacency list is a data structure that is used to represent a graph, where each element of the list represents a node of the graph and contains a list of the nodes it is connected to.\n\n3. Then it calls the helper function `"minTimeToCollectApples"` which takes four arguments:\n\n- index: the current node being processed\n- adj: the adjacency list representation of the tree\n- hasApple: a list of booleans indicating whether each node has an apple or not\n- parent: the parent of the current node\n\nThe function starts by initializing a variable "total" to zero. It then iterates over all the neighbors of the current node (excluding the parent) and recursively calls the function on each of the neighbors. This way it explores all the path from the current node to all the children nodes.\n\nThen, if the current node is not the root of the tree and it has an apple or any of its children has an apple, it adds 2 to the "total" variable as this represent that we need to take 2 steps: one step to reach the apple and one step back to the parent.\n\nFinally, it returns the "total" variable.\n\n# Code\n```\nclass Solution {\n    // Function to find the minimum time to collect all apples\n    public int minTime(int n, int[][] edges, List<Boolean> hasApple) {\n        // Create an adjacency list to represent the tree\n        List<List<Integer>> adj = new ArrayList<>();\n        for(int i = 0; i < n; i++){\n            adj.add(new ArrayList<>());\n        }\n        // populate the adjacency list\n        for(int [] edge : edges){\n            adj.get(edge[0]).add(edge[1]);\n            adj.get(edge[1]).add(edge[0]);\n\n        }\n        // call to helper function to find the minimum time\n        return minTimeToCollectApples(0, adj, hasApple, 0);\n    }\n    // Helper function\n    int minTimeToCollectApples(int index, List<List<Integer>> adj, List<Boolean> hasApple, int parent){\n        // variable to keep track of total time\n        int total = 0;\n        // for each neighbor of current node\n        for(int nbr : adj.get(index)){\n            // if the neighbor is the parent node, then we skip\n            if (nbr == parent)\n             continue;\n            // we recursively call the helper function for each neighbor\n            total += minTimeToCollectApples(nbr, adj, hasApple, index);\n        }\n        // If current node is not the root (0th) node, and it has an apple or any of its descendant has\n        //  then we need to add 2 time for moving to and from it\n        if( index != 0 && (hasApple.get(index) || total > 0))\n          total += 2;\n        return total;\n    }\n}\n\n```
['Java']