给定一个字符串S ，任务是计算给定字符串中反向双音子串的数量。
Reverse bitonic substring: A string in which the ASCII values of the characters of the string follow any of the following patterns:
- Strictly Increasing
- Strictly decreasing
- Decreasing and then increasing
例子：
Input: S = “bade”
Output: 10
Explanation:
All possible substrings of length 1, {“b”, “a”, “d”, “e”} are always reverse bitonic.
Substrings of length 2 which are reverse bitonic are {“ba”, “ad”, “de”}.
Substrings of length 3 which are reverse bitonic are {“bad “, “ade”}.
Only substring of length 4 which is reverse bitonic is “bade”.
Therefore, the count of reverse bitonic substrings is 10.
Input: S = “abc”
Output: 6
方法 ：
方法是生成给定字符串的所有可能的子串，并对每个子串按照以下步骤解决问题：
- 遍历字符串，对于每个字符，检查下一个字符的 ASCII 值是否小于当前字符的 ASCII 值。
- 如果在任何时候，下一个字符的 ASCII 值大于当前字符的 ASCII 值，从该索引开始遍历，从现在开始，对于每个字符，检查下一个字符的 ASCII 值是否大于 ASCII 值当前字符与否。
- 如果在任何时候，到达子串末尾之前下一个字符的 ASCII 值小于当前字符的 ASCII 值，则忽略该子串。
- 如果到达子字符串的末尾，则增加count 。
- 对所有子串完成上述所有步骤后，打印count的最终值。
下面是上述方法的实现：
C++
// C++ Program to implement
// the above approach
#include
using namespace std;
// Function to calculate the number
// of reverse bitonic substrings
int CountsubString(char str[], int n)
{
// Stores the count
int c = 0;
// All possible lengths of substrings
for (int len = 1; len <= n; len++) {
// Starting point of a substring
for (int i = 0; i <= n - len; i++) {
// Ending point of a substring
int j = i + len - 1;
char temp = str[i], f = 0;
// Condition for reverse
// bitonic substrings of
// length 1
if (j == i) {
c++;
continue;
}
int k = i + 1;
// Check for decreasing sequence
while (temp > str[k] && k <= j) {
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j) {
c++;
f = 2;
}
// For increasing sequence
while (temp < str[k] && k <= j
&& f != 2) {
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j && f != 2) {
c++;
f = 0;
}
}
}
// Return the number
// of bitonic substrings
return c;
}
// Driver Code
int main()
{
char str[] = "bade";
cout << CountsubString(str, strlen(str));
return 0;
} Java
// Java program to implement
// the above approach
class GFG{
// Function to calculate the number
// of reverse bitonic substrings
public static int CountsubString(char[] str,
int n)
{
// Stores the count
int c = 0;
// All possible lengths of substrings
for(int len = 1; len <= n; len++)
{
// Starting point of a substring
for(int i = 0; i <= n - len; i++)
{
// Ending point of a substring
int j = i + len - 1;
char temp = str[i], f = 0;
// Condition for reverse
// bitonic substrings of
// length 1
if (j == i)
{
c++;
continue;
}
int k = i + 1;
// Check for decreasing sequence
while (temp > str[k] && k <= j)
{
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j)
{
c++;
f = 2;
}
// For increasing sequence
while (k <= j && temp < str[k] &&
f != 2)
{
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j && f != 2)
{
c++;
f = 0;
}
}
}
// Return the number
// of bitonic substrings
return c;
}
// Driver code
public static void main(String[] args)
{
char str[] = { 'b', 'a', 'd', 'e' };
System.out.println(CountsubString(
str, str.length));
}
}
// This cdoe is contributed by divyeshrabadiya07Python3
# Python3 program to implement
# the above approach
# Function to calculate the number
# of reverse bitonic substrrings
def CountsubString(strr, n):
# Stores the count
c = 0
# All possible lengths of substrrings
for len in range(n + 1):
# Starting poof a substrring
for i in range(n - len):
# Ending poof a substrring
j = i + len - 1
temp = strr[i]
f = 0
# Condition for reverse
# bitonic substrrings of
# length 1
if (j == i):
c += 1
continue
k = i + 1
# Check for decreasing sequence
while (k <= j and temp > strr[k]):
temp = strr[k]
k += 1
# If end of substrring
# is reache
if (k > j):
c += 1
f = 2
# For increasing sequence
while (k <= j and f != 2 and
temp < strr[k]):
temp = strr[k]
k += 1
# If end of substrring
# is reached
if (k > j and f != 2):
c += 1
f = 0
# Return the number
# of bitonic substrrings
return c
# Driver Code
if __name__ == '__main__':
strr = "bade"
print(CountsubString(strr, len(strr)))
# This code is contributed by mohit kumar 29C#
// C# program to implement
// the above approach
using System;
class GFG{
// Function to calculate the number
// of reverse bitonic substrings
public static int CountsubString(char[] str,
int n)
{
// Stores the count
int c = 0;
// All possible lengths of substrings
for(int len = 1; len <= n; len++)
{
// Starting point of a substring
for(int i = 0; i <= n - len; i++)
{
// Ending point of a substring
int j = i + len - 1;
char temp = str[i], f = '0';
// Condition for reverse
// bitonic substrings of
// length 1
if (j == i)
{
c++;
continue;
}
int k = i + 1;
// Check for decreasing sequence
while (temp > str[k] && k <= j)
{
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j)
{
c++;
f = '2';
}
// For increasing sequence
while (k <= j && temp < str[k] &&
f != '2')
{
temp = str[k];
k++;
}
// If end of substring
// is reached
if (k > j && f != 2)
{
c++;
f = '0';
}
}
}
// Return the number
// of bitonic substrings
return c;
}
// Driver code
public static void Main(String[] args)
{
char []str = { 'b', 'a', 'd', 'e' };
Console.WriteLine(CountsubString(
str, str.Length) - 1);
}
}
// This code is contributed by amal kumar choubeyJavascript
输出：
10时间复杂度： O(N)
辅助空间： O(1)
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