计算以字符“ A”开始并以字符“ X”结束的子字符串 [英] Counting substring that begin with character 'A' and ends with character 'X'

问题描述

PYTHON QN：
仅使用一个循环，如何设计一种算法，计算以字符 A 开头并以字符 X ？例如，给定输入字符串 CAXAAYXZA ，有四个子字符串以 A 开头，以 X ，即： AX ， AXAAYX ， AAYX 和 AYX 。

PYTHON QN: Using just one loop, how do I devise an algorithm that counts the number of substrings that begin with character A and ends with character X? For example, given the input string CAXAAYXZA there are four substrings that begin with A and ends with X, namely: AX, AXAAYX, AAYX, and AYX.

例如：

>>>count_substring('CAXAAYXZA')
4

推荐答案

由于您未指定语言，因此我正在使用c ++ ish

Since you didn't specify a language, im doing c++ish

int count_substring(string s)
{
  int inc = 0;
  int substring_count = 0;

  for(int i = 0;i < s.length();i++)
  {
     if(s[i] == 'A') inc++;
     if(s[i] == 'X') substring_count += inc;
  }
  return substring_count;
}

和Python

def count_substring(s):
   inc = 0
   substring_count = 0
   for c in s:
      if(c == 'A'): inc = inc + 1
      if(c == 'X'): substring_count = substring_count + inc
   return substring_count

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