Longest Common Prefix

longestCommonPrefix.js

/**
 * @param {string[]} strs
 * @return {string}
 */
var longestCommonPrefix = function(strs) {
    if(strs.length == 0) return "";
    if(strs.length == 1) return strs[0];

    let prefix = strs[0];
    let prefixLen = prefix.length;
    
    for(let i=1; i<strs.length; i++) {
        while(prefix != strs[i].slice(0, prefixLen)) {
            prefixLen -= 1;
            if(prefixLen == 0) return "";
            prefix = prefix.slice(0, prefixLen);
        }   
    }

    return prefix;
};

// store the first element as a prefix check
// run a loop through the array and check whether the current prefix string equals the string in current iteration
// if not, then remove the last character from both the strings and check again
// do this till either the strings become empty or we find a match 
// if the strings are empty return empty string because there is no longest common prefix
// if we find a match, store it as the new prefix and move on to the next iteration
// finally return the prefix after the loop is done

// Time: O(n * m)  n --> length of array; m --> length of first string in the array
// Space: O(m)