14. Longest Common Prefix

class Solution {
    public String longestCommonPrefix(String[] strs) {
        
        if (strs.length == 0) {
            return "";
        }
        
        // loop every index in string
        for (int i = 0; i < strs[0].length(); i++) {
            char cur = strs[0].charAt(i);
            
            // loop every string
            for (int j = 0; j < strs.length; j++) {
                if (strs[j].length() == i || cur != strs[j].charAt(i)) {
                    return strs[0].substring(0, i);
                }
            }
        }
        return strs[0];
    }
}

class Solution {
    // Consider edge cases:
    // ["a"], ["a", ""], ["a", "b"]
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) {
            return "";
        }
        if (strs.length == 1) {
            return strs[0];
        }
        String curCommon = strs[0];
        for (int i = 1; i < strs.length; i++) {
            curCommon = getCommonPrefix(curCommon, strs[i]);
            if (curCommon == "") {
                return curCommon;
            }
        }
        return curCommon;
    }
    
    private String getCommonPrefix (String str1, String str2) {
        char[] char1 = str1.toCharArray();
        char[] char2 = str2.toCharArray();
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < char1.length && i < char2.length; i++) {
            if (char1[i] == char2[i]) {
                sb.append(char1[i]);
            } else {
                break;
            }
        }
        return sb.toString();
    }
}