leetcode 14. Longest Common Pref

/**
 * @param {string[]} strs
 * @return {string}
 */
var longestCommonPrefix = function(strs) {
    if (!strs) {
        return undefined;
    }
    var flag = false;
    var minSize = undefined;
    if (strs.length == 0) {
        return "";
    }
    if (strs.length == 1) {
        return strs[0];
    }
    for (var i = 0; i < strs.length; i++) {
        var s = strs[i];
        if (!!s) {
            flag = true;
            if (minSize === undefined || s.length < minSize) {
                minSize = s.length;
            }
        }
    }
    if (!flag) {
        return "";
    }
    var prefix = "";
    for (var i = 0; i < minSize; i++) {
        var current = strs[0].substr(0, i + 1);
        for (var j = 1; j < strs.length; j++) {
            var temp = strs[j].substr(0, i + 1);
            if (temp != current) {
                return prefix;
            }
        }
        prefix = current;
    }
    return prefix;
};