ApproveTx.sol

address bob = 0x237C8Aea434dE4784d23d145069c6D0Bef629A19 // Give Me Ether
IERC20 token;
uint N = 3 ether
uint M = 1 ether
/* 👩 Alice, 👨 Bob */

/* Bad */
/* FROM  | 🕛  | ORDER　　 | BLOCK |  GAS    */
/*  👩   | 0s  |   1    |   N   | 100,000 */ token.approve(bob,N); 
/*  👩   | 20s |   2    |  N+1  | 100,000 */ token.approve(bob,M);
/*  👨   | 21s |   3    |  N+1  | 50,000  */ token.transferFrom(bob,N); // Failed
/*  👨   | 60s |   4    |  N+2  | 50,000  */ token.transferFrom(bob,M);

/* Better */
/* FROM  | 🕛  | ORDER　　 | BLOCK |  GAS    */
/*  👩   | 0s  |   1    |   N   | 100,000 */ token.approve(bob,N); 
/*  👩   | 20s |   3    |  N+1  | 100,000 */ token.approve(bob,M);
/*  👨   | 21s |   2    |  N+1  | 500,000 */ token.transferFrom(bob,N); // Sucess
/*  👨   | 60s |   4    |  N+2  | 50,000  */ token.transferFrom(bob,M);