Random shuffling algorithm and random selection algorithm

1. Random shuffling Algorithm

Problem description: sorts the elements in an ordered set in random order.

Solution:

For I: = 1 to n do swap (A [I], a [random (1, N)]); // merge, but not really random

For
I: = 1 to n do swap (A [I], a [random (I, n)]); // real random Algorithm

2. Random selection algorithm

How to extract M random numbers from N

Solution: the probability of the first number being extracted is 1, the second is 1/2, the third is 1/3, and so on, the nth number is 1/N, the probability of each number being extracted is 1/N.

The first M count is the M count at initialization. When the nth number is reached, the random number is located in 1 ~ N. If the random number is in m, replace the number and the random number until all data is traversed. The probability of each number being extracted is M/N.