Step-by-step write algorithm (number of returns)

Original: Step-by-step write algorithm (number of returns)

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The concept of the number of returns is interesting, that is, there is a string str, the length is N, now index begins to traverse from 0->INDEX/2, then str[index] = Str[n-1-index], then this data is what we usually say the number of returns. For example a = "A" is a return number, a = "ABA" is the number of returns, A = "Strarts" is also the number of returns. Because the problem is relatively simple, many companies like to use it to check the programmer's basic programming skills. Not only that, it also examines the programmer's consideration of whether the problem is well-conceived and whether to consider it from different perspectives.

For example, now we want the characters in the string to be lowercase letters or uppercase letters, not other characters, how to write? Friends can try.

int issymbolright (const char* str, int length) {int Index;char symbol;for (index = 0; index < length; index++) {symbol = s Tr[index];if (Symbol >= ' a ' && symbol <= ' z ' | | symbol >= ' a ' && symbol <= ' z ')        continue;
   return 0;} return 1;} int isanagramornot (const char* str, int length) {int index;if (NULL = = Str | | 0 = = length) return 0;if (!issymbolright (str, le ngth)) return 0;for (index = 0; index < (length >> 1); index + +) {if (Str[index]! = str[length-1-index]) return 0; return 1;}

The above method is only a traditional comparison method, if the interviewer said the interview with a recursive method how to calculate it? Friends can try again.

int _isanagramornot (const char* str, int length) {if (0 = = Length | | 1 = = length) return 1;return (str[0] = = Str[length-1]) ? _isanagramornot (str +1, length-2): 0;} int isanagramornot (const char* str, int length) {if (NULL = = Str | | 0 = = length) return 0;if (!issymbolright (str, length)) Retu RN 0;return _isanagramornot (str, length);}

Then, we will increase the difficulty a little more, if the comparison of data a lot, there are 10 million, then how to use multi-core programming to improve the speed of data processing?

int _isanagramornot (const char* STR, int start, int end, int length) {int Index;char symbol;for (index = 0; index < lengt H  Index + +) {if (Str[start + index]! = str[end-1-index]) return 0;symbol = Str[start + index];if (symbol >= ' a ' && Symbol <= ' Z ' | | Symbol >= ' A ' && symbol <= ' Z ') Continue;return 0;} return 1;} int isanagramornot (const char* str, int length) {int index;int start[2];int end[2];int result[2] = {0};if (NULL = = str | | 0 = = length) return 0;start[0] = 0;start[1] = length >> 2;end[0] = length;end[1] = length-(length >>2); #pragma OMP parallel forfor (index = 0; index < 2; index + +) Result[index] = _isanagramornot (str, start[index], End[index], lengt H >> 2); return (Result[0] && result[1])? 1:0;}

Summarize:

(1) From the above topics can be seen, even if very simple topic, you can also examine the total ability of candidates

(2) To improve the efficiency of the algorithm implementation of a lot of ways, friends usually can pay more attention to the class, accumulate

(3) The execution of all algorithms is based on correctness and robustness, and must be built on the basis of adequate testing.

Step-by-step write algorithm (number of returns)