1971. Find if Path Exists in Graph

class Solution {
    public boolean validPath(int n, int[][] edges, int source, int destination) {
        if(source == destination) return true;
        Graph g = new Graph(n);
        
        for(int i = 0 ; i < edges.length; i++){
            g.addEdge(edges[i][0],edges[i][1]);
            g.addEdge(edges[i][1],edges[i][0]);
        }
        boolean[] visited = new boolean[n];
        
        Queue<Integer> q = new LinkedList<Integer>();
        q.add(source);
        visited[source] =true;
        while(!q.isEmpty()){
            int current = q.poll();
             Iterator<Integer> i = g.adj[current].listIterator();
            while (i.hasNext())
            {
                int next = i.next();
                if(next == destination) return true;
                if (!visited[next])
                {
                    visited[next] = true;
                    q.add(next);
                   
                }
            }
            
            
        }
        
        return false;
    }
    class Graph
{
    private int V;   // No. of vertices
    private LinkedList<Integer> adj[]; //Adjacency Lists
 
    // Constructor
    Graph(int v)
    {
        V = v;
        adj = new LinkedList[v];
        for (int i=0; i<v; ++i)
            adj[i] = new LinkedList();
    }
 
    // Function to add an edge into the graph
    void addEdge(int v,int w)
    {
        adj[v].add(w);
    }
}
}

1470. Shuffle the Array

class Solution {
    public int[] shuffle(int[] nums, int n) {
        int[] out = new int[nums.length];
        int x =0;
        int y = nums.length/2;
        for(int i = 0; i < nums.length; i++){
            if(i % 2 == 0){
                out[i] = nums[x];
                x++;
            }else{
                out[i] = nums[y];
                y++;
            }
        }
        return out;
    }
}

122. Best Time to Buy and Sell Stock II

class Solution {
    public int maxProfit(int[] prices) {
        int profit = 0;
        for (int i = 0; i < prices.length-1; i++){
            if(prices[i+1] > prices[i]) profit+= (prices[i+1] - prices[i]);
        }
        return profit;
    }
}

11. Container With Most Water

class Solution {
    public int maxArea(int[] height) {
        int maxArea =  Integer.MIN_VALUE;
        int l = 0;
        int r = height.length - 1;
        while(l < r){
            maxArea = Integer.max(maxArea, Integer.min(height[l],height[r])*(r-l));
            if(height[l] < height[r]) l++;
                else r--;
        }
        return maxArea;
    }
}

62. Unique Paths

Dynamic Programming

class Solution {
    public int uniquePaths(int m, int n) {
        if(n ==1 && m ==1) return 1;
        int[][] grid = new int[m][n];

        for(int i = 1;  i <m; i++){
         grid[i][0] = 1;  
        }
    
        for(int i = 1; i < n; i++){
            grid[0][i] = 1;
        }
        for(int i = 1; i < m; i++){
            for(int j = 1; j < n; j++){
                grid[i][j] =grid[i-1][j] + grid[i][j-1];
            }
        }
        return grid[m-1][n-1];
    }
}

605. Can Place Flowers

class Solution {
    public boolean canPlaceFlowers(int[] flowerbed, int n) {
        if(flowerbed.length == 1 && flowerbed[0] == 0) n--;
        for(int i = 0; i < flowerbed.length; i++){
            if(i ==0 && flowerbed[i] == 0 && i+1 <  flowerbed.length && flowerbed[i+1] == 0){
                flowerbed[i] = 1;
                n--;
            }else if( i == flowerbed.length -1 && 
                     flowerbed[i] == 0 && i-1 >= 0 &&
                     flowerbed[i-1] == 0){
            flowerbed[i] = 1;
                n--;
            }
            else if(flowerbed[i] == 0  &&
                    i-1 >= 0 &&
                    flowerbed[i-1] == 0  &&
                    i+1 <  flowerbed.length &&
                    flowerbed[i+1] == 0){
                flowerbed[i] = 1;
                n--;
            } 
        }
        if(n <= 0) return true;
        else return false;
    }
}

Birthday Cake Candles

    public static int birthdayCakeCandles(List<Integer> candles) {
    // Write your code here
             TreeMap<Integer,Integer> f = new TreeMap<>();
       for (Integer a: candles)
           f.put(a,f.getOrDefault(a, 0)+1);
       return f.lastEntry().getValue();
    }