About the choice of infinite mass

When solving a problem, you usually have a situation where you are set to infinity. This time is usually set with 0x7fffffff, he is the computer 32-bit integer maximum number, the equivalent of Int_max. But in many cases this setting is not optimal and can lead to bugs because we sometimes want infinity + infinity = infinity, For example, in the prim algorithm or the Dijstra algorithm on the edge of the slack operation, this time Int_max arbitrarily add a number will overflow, resulting in a wrong result.

In fact, the other number 0x3f3f3f3f decimal is 1061109567, which is the same order of magnitude as 0x7fffffff. We use the 0x3f3f3f to replace the 0x7fffffff can satisfy infinity and infinity is still infinite conditions, so as to avoid catastrophic errors. In addition 0x3f3f3f can also use the Memset function to bulk assign values, such as to set the array dis[] to infinity:

memset (dis,0x3f,sizeof (dis));

if the array dis is a long long, the above statement sets the DIS to 4557430888798830399, and if the dis is of type int, the above statement sets the dis to 1061109567 whether in long or int, Two infinite and will not explode. The above 0x3f is a byte 0x3f3f3f3f altogether there are four such bytes. In general, 0X3F3F3F3F is a good choice for setting infinity.              

About the choice of infinite mass