Checking to see what stocks billionaires are buying is a great way to find new investment ideas.Looking at what billionaire hedge fund managers are doing is a great idea for investors, as it gives you a chance to see what top minds in the investing world think about trends like artificial intelligence (AI). If these massive funds start to sell out of their positions, it could be a warning sign for investors that the party is over. But if they're increasing their stakes, it could be a bullish indicator.Three ...