Path Existence in a Graph

Write a program to determine whether there exists a path between two nodes in an undirected graph. The graph is defined by its number of nodes and a list of edges. The program must output 'YES' if a path exists and 'NO' otherwise. Input format: - The first line contains two integers, n (1 ≤ n ≤ 1000) and m (0 ≤ m ≤ 10,000). - The second line contains two integers a and b, the start and end nodes. - The next m lines contain the edges as two integers u and v. Output format: - 'YES' if a path exists from a to b, 'NO' otherwise. Example: Input: 5 4 1 5 1 2 2 3 3 4 4 1 Output: YES