How to write C code for fast algorithm of full arrangement of letters
This article introduces how to write a fast algorithm C code for full arrangement of letters. The content is very detailed. Interested friends can use it for reference. I hope it will be helpful to you.
All permutations, such as the letter ABC, all permutations have A, AB,AC,ABC,ACB,B,BA,BC,BAC,BCA,C,CA,CB,CAB,CBA.
/ / the principle is to insert, insert new characters at all positions in a string.
/ / for example, AB is inserted into C, where there is 1A2B3, and CAB ACB ABC is formed after insertion.
Char * AllList (char * str, int * pNum)
... {
Int i, j, k, n
Int len = strlen (str)
Int Total = 0
Int count, oldcount
Int size
Char * Buf
Char * p, * p1
If (len > 10) return NULL
/ / calculate the total number of combinations
For (I = 0, j = 1; I len; iTunes +)
... {
J * = (len-I)
Total + = j
}
/ / create a two-dimensional array to store all combinations
Size = len + 1
If ((Buf = (char *) malloc (Total * size)) = = NULL)
... {
Return NULL
}
For (k = 0, count = 0; k len; kits +) / / all characters to be inserted
... {
Oldcount = count
P = Buf
P1 = Buf + count * size
For (I = 0; I oldcount; iTunes, p + = size) / / is inserted into all strings to form a new string
... {
N = strlen (p)
For (j = 0; j n; jblocks, count++, p1 + = size) / / insert at all positions of the string
... {
Memcpy (p1, p, n)
P1 [n] = p1 [j]
P1 [j] = str [k]
P1 [n + 1] ='
Arrange 10 letters on my machine for about 0.5 seconds.
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