If I make this silly mistake again/ (ㄒoㄒ)/~~

1. When multiplying modulo , Remember to take the module first and then multiply , Don't take the mold while multiplying , Otherwise, it may explode .

eg: HDU6961 The data range reaches 1e18, And the answer is   2*(n*(n-1))^2, If written 2*n%mod*(n-1)%mod*n%mod*(n-1)%mod It's likely to explode in the middle of a multiplication operation long long .

2. When it comes to the multiplication and division of floating-point numbers, we must pay attention to the problem of accuracy .

eg: Cattle guest 2021 Summer multi school 3 Of F, The process involves 8*(3-8/3)==24？ There will be accuracy problems , Take advantage of x-y<=1e6 This method will be more intuitive and effective .