给定字符串S由小写和大写字母组成,任务是找到具有相等数量的小写和大写字母的子串的数量。
例子:
Input: S = “gEEk”
Output: 3
Explanation:
The following are the substrings having an equal number of lowercase and uppercase letters:
- “gE”
- “gEEk”
- “Ek”
Therefore, the total count of substrings is 3.
Input: S = “WomensDAY”
Output: 4
朴素方法:解决给定问题的最简单方法是生成给定字符串S 的所有可能子字符串,如果该子字符串包含相同数量的小写字母和大写字母,则将子字符串的计数加1 。检查所有子字符串后,打印计数值作为结果。
时间复杂度: O(N 3 )
辅助空间: O(1)
有效的方法:可以通过将每个小写和大写字母分别视为1和-1来解决给定的问题,然后找到总和为0的子数组的计数。请按照以下步骤解决问题:
- 初始化一个 HashMap,比如存储所有前缀总和的频率的M。
- 初始化一个变量,比如currentSum为0和res为0 ,分别存储每个前缀的总和和结果子串的计数。
- 遍历字符串并执行以下步骤:
- 如果当前字符为大写,则将currentSum的值增加1 。否则,将currentSum的值减少-1 。
- 如果currentSum 的值为0 ,则将res的值增加1 。
- 如果currentSum的值存在于映射M 中,则将res的值增加M[currentSum] 。
- 将 HashMap M中currentSum的频率增加1 。
- 完成上述步骤后,打印res的值作为结果。
下面是上述方法的实现:
C++
// C++ program for the above approach
#include
using namespace std;
// Function to find the count of
// substrings having an equal number
// of uppercase and lowercase characters
int countSubstring(string& S, int N)
{
// Stores the count of prefixes
// having sum S considering uppercase
// and lowercase characters as 1 and -1
unordered_map prevSum;
// Stores the count of substrings
// having equal number of lowercase
// and uppercase characters
int res = 0;
// Stores the sum obtained so far
int currentSum = 0;
for (int i = 0; i < N; i++) {
// If the character is uppercase
if (S[i] >= 'A' and S[i] <= 'Z') {
currentSum++;
}
// Otherwise
else
currentSum--;
// If currsum is o
if (currentSum == 0)
res++;
// If the current sum exists in
// the HashMap prevSum
if (prevSum.find(currentSum)
!= prevSum.end()) {
// Increment the resultant
// count by 1
res += (prevSum[currentSum]);
}
// Update the frequency of the
// current sum by 1
prevSum[currentSum]++;
}
// Return the resultant count of
// the subarrays
return res;
}
// Driver Code
int main()
{
string S = "gEEk";
cout << countSubstring(S, S.length());
return 0;
}
Java
// Java program for the above approach
import java.util.HashMap;
class GFG{
// Function to find the count of
// substrings having an equal number
// of uppercase and lowercase characters
static int countSubstring(String S, int N)
{
// Stores the count of prefixes
// having sum S considering uppercase
// and lowercase characters as 1 and -1
HashMap prevSum = new HashMap<>();
// Stores the count of substrings
// having equal number of lowercase
// and uppercase characters
int res = 0;
// Stores the sum obtained so far
int currentSum = 0;
for(int i = 0; i < N; i++)
{
// If the character is uppercase
if (S.charAt(i) >= 'A' && S.charAt(i) <= 'Z')
{
currentSum++;
}
// Otherwise
else
currentSum--;
// If currsum is 0
if (currentSum == 0)
res++;
// If the current sum exists in
// the HashMap prevSum
if (prevSum.containsKey(currentSum))
{
// Increment the resultant
// count by 1
res += prevSum.get(currentSum);
}
// Update the frequency of the
// current sum by 1
prevSum.put(currentSum,
prevSum.getOrDefault(currentSum, 0) + 1);
}
// Return the resultant count of
// the subarrays
return res;
}
// Driver Code
public static void main(String[] args)
{
String S = "gEEk";
System.out.println(countSubstring(S, S.length()));
}
}
// This code is contributed by abhinavjain194
Python3
# Python3 program for the above approach
# Function to find the count of
# substrings having an equal number
# of uppercase and lowercase characters
def countSubstring(S, N):
# Stores the count of prefixes
# having sum S considering uppercase
# and lowercase characters as 1 and -1
prevSum = {}
# Stores the count of substrings
# having equal number of lowercase
# and uppercase characters
res = 0
# Stores the sum obtained so far
currentSum = 0
for i in range(N):
# If the character is uppercase
if (S[i] >= 'A' and S[i] <= 'Z'):
currentSum += 1
# Otherwise
else:
currentSum -= 1
# If currsum is o
if (currentSum == 0):
res += 1
# If the current sum exists in
# the HashMap prevSum
if (currentSum in prevSum):
# Increment the resultant
# count by 1
res += (prevSum[currentSum])
# Update the frequency of the
# current sum by 1
if currentSum in prevSum:
prevSum[currentSum] += 1
else:
prevSum[currentSum] = 1
# Return the resultant count of
# the subarrays
return res
# Driver Code
if __name__ == '__main__':
S = "gEEk"
print(countSubstring(S, len(S)))
# This code is contributed by bgangwar59
C#
// C# program for the above approach
using System;
using System.Collections.Generic;
class GFG{
// Function to find the count of
// substrings having an equal number
// of uppercase and lowercase characters
static int countSubstring(String S, int N)
{
// Stores the count of prefixes
// having sum S considering uppercase
// and lowercase characters as 1 and -1
Dictionary prevSum = new Dictionary();
// Stores the count of substrings
// having equal number of lowercase
// and uppercase characters
int res = 0;
// Stores the sum obtained so far
int currentSum = 0;
for(int i = 0; i < N; i++)
{
// If the character is uppercase
if (S[i] >= 'A' && S[i] <= 'Z')
{
currentSum++;
}
// Otherwise
else
currentSum--;
// If currsum is 0
if (currentSum == 0)
res++;
// If the current sum exists in
// the Dictionary prevSum
if (prevSum.ContainsKey(currentSum))
{
// Increment the resultant
// count by 1
res += prevSum[currentSum];
prevSum[currentSum] = prevSum[currentSum] + 1;
}
else
prevSum.Add(currentSum, 1);
}
// Return the resultant count of
// the subarrays
return res;
}
// Driver Code
public static void Main(String[] args)
{
String S = "gEEk";
Console.WriteLine(countSubstring(S, S.Length));
}
}
// This code is contributed by Princi Singh
Javascript
输出:
3
时间复杂度: O(N)
辅助空间: O(1)
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