JavaScript Program Count number of Equal Pairs in a String
Last Updated :
02 Nov, 2023
In this article, we are going to learn how can we count a number of equal pairs in a string. Counting equal pairs in a string involves finding and counting pairs of consecutive characters that are the same. This task can be useful in various applications, including pattern recognition and data analysis.
Examples:
Input: 'pqr'
Output: 3
Explanation:
3 pairs that are equal are (p, p), (q, q) and (r, r)
Input: 'HelloWorld'
Output: 18
Approach 1: Naive Approach
The straightforward method involves using two nested loops to iterate through the string, identifying all pairs, and maintaining a count of these pairs.
Example:
Javascript
function fun(str) {
let strLength = str.length;
let pairCount = 0;
for (let i = 0; i < strLength; i++) {
for (let j = 0; j < strLength; j++) {
if (str[i] == str[j]) {
pairCount++;
}
}
}
return pairCount;
}
let str = "geeksforgeeks";
console.log(fun(str));
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Time Complexity: O(n2), n is the length of input string
Space Complexity: O(1)
Approach2: Efficient appraoch
- In this approach, We must efficiently determine the count of distinct pairs of characters in linear time.
- Notably, pairs like (x, y) and (y, x) are treated as distinct.
- To accomplish this, we employ a hash table to record the occurrences of each character. If a character appears twice, it corresponds to 4 pairs: (i, i), (j, j), (i, j), and (j, i).
- By utilizing a hashing mechanism, we keep track of the frequency of each character, and for each character, the count of pairs will be the square of its frequency.
- The hash table will have a length of 256 since there are 256 distinct characters.
Example: This example shows the use of the above-explined approach.
Javascript
const MAX = 256
function fun(str) {
let charCount = new Array(MAX).fill(0)
for (let i = 0; i < str.length; i++)
charCount[str.charCodeAt(i) - 97] += 1
let pairCount = 0
for (let i = 0; i < MAX; i++)
pairCount += charCount[i] * charCount[i]
return pairCount
}
let str = "pqr"
console.log(fun(str))
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Time Complexity: O(n), n is the length of input string
Space Complexity: O(1)
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