• strs[0] must be a superset of final prefix.
  • Check all other strings if they contain strs[0]; if not, substring it until satisfied.
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class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs == null || strs.length == 0) return "";
        String pre = strs[0]; 
        
        for (int i = 1; i < strs.length; ++i) {
            while (strs[i].indexOf(pre) != 0) {
                pre = pre.substring(0, pre.length() - 1);
            }
        }
        
        return pre;
    }
}