LongestCommonSubstring.js

function LongestCommonSubstring(word1,word2){
    var max = 0;
    var index = 0;
    var lcsArr = new Array(word1.length+1);
    for (var i = 0; i <= word1.length+1; ++i) {
        lcsArr[i] = new Array(word2.length+1);
        for (var j = 0; j <= word2.length+1; ++j) {
            lcsArr[i][j] = 0;
        }
    }

    for (var i = 0; i <= word1.length; ++i) {
        for (var j = 0; j <= word2.length; ++j) {
            if (i == 0 || j == 0) {
                lcsArr[i][j] = 0;
            }
            else {
                if (word1[i-1] == word2[j-1]) {
                    lcsArr[i][j] = lcsArr[i-1][j-1] + 1;
                }
                else {
                    lcsArr[i][j] = 0;
                }
            }
            if (max < lcsArr[i][j]) {
                max = lcsArr[i][j];
                index = i;
            }
        }
    }

    var str = '';
    if(max == 0){ //no common string
        return '';
    }else{
        for(var i = index - max; i <=max; i++){
            str += word2[i];
        }

        return str;
    }
}
var str1 = "raven";
var str2 = "havoc";

console.log(LongestCommonSubstring(str1,str2)); //av