这个算法怎么是这样的？

Question

Answer 1

https://wk.baidu.com/view/e676474da417866fb84a8e96.html?fr=aladdin31713&ind=1&callWelfare=1&wiseType=voucher&failUrlType=1&wiseQuery=%E8%BE%97%E8%BD%AC%E7%9B%B8%E9%99%A4%E6%B3%95%E6%B1%82%E6%9C%80%E5%A4%A7%E5%85%AC%E7%BA%A6%E6%95%B0&ssid=0&from=2001a&uid=0&pu=usm@4,sz@1320_1003,ta@iphone_2_8.1_1_87.6&bd_page_type=1&baiduid=1602D3EDBB686EE5A3EA18493EC19A05&tj=8lx_1_0_10_l1@4,sz@1320_1003,ta@iphone_2_8.1_1_87.6&bd_page_type=1&baiduid=1602D3EDBB686EE5A3EA18493EC19A05&tj=8lx_1_0_10_l1