Question

How to count the number of non-overlapping instances of a substring in a string in JavaScript

Answer 1

function countNonOverlappingOccurrences(str, substr) {
    if (substr === "") return 0;
 
    let count = 0;
    let offset = str.indexOf(substr);
 
    while (offset !== -1) {
        count++;
        offset = str.indexOf(substr, offset + substr.length);
    }
 
    return count;
}
 
const s = "go java phphp rust c pphpp c++ phpphp python php phphp";
 
console.log(countNonOverlappingOccurrences(s, "php"));
 
 
    
/*
run:
    
6
 
*/

 

70+ SQL courses for beginners and professionals

Answer 2

function countNonOverlappingOccurrences(str, substr) {
    return (str.length - str.replace(new RegExp(substr, "gi"), "").length) / substr.length;
}
 
const s = "go java phphp rust c pphpp c++ phpphp python php phphp";
 
console.log(countNonOverlappingOccurrences(s, "php"));
 
 
    
/*
run:
    
6
 
*/
 

 

70+ SQL courses for beginners and professionals

Answer 3

// Non‑overlapping occurrences are matches of a substring that do not reuse any of
// the same characters. Once one match is counted, the next search must begin
// after that match ends.

function count_non_overlapping(haystack, needle) {
    /*
       Count how many times 'needle' appears in 'haystack' without overlapping.
       The algorithm:
         • Use indexOf() to locate the next occurrence.
         • Each time a match is found, move the search index forward
           by the full length of the matched substring.
         • This ensures no characters are reused between matches.
    */

    let count = 0;
    let index = 0;  // current search position in the main string

    // Continue searching until indexOf() returns -1 (meaning: no more matches)
    while (true) {
        // Find the next occurrence starting at the current index
        const pos = haystack.indexOf(needle, index);

        if (pos === -1) {
            // No more matches found
            break;
        }

        // We found a match, so increment the count
        count++;

        // Move index forward by the length of the needle
        // This ensures the next search begins *after* the matched substring
        index = pos + needle.length;
    }

    return count;
}


// ---------------------------------------------------------------
// Demonstration using the string provided in the instructions:
const s = 'go java phphp rust c pphpp c++ phpphp python php phphp';
const substring = 'php';

// Count non-overlapping occurrences
const result = count_non_overlapping(s, substring);

console.log("Non-overlapping occurrences:", result);



/*
run:

Non-overlapping occurrences: 6

*/

 

70+ SQL courses for beginners and professionals