leetcode03

class Solution {
    public String longestCommonPrefix(String[] strs) {
        if (strs.length < 1) {
            return "";
        }

     List<char[]> chars = new ArrayList<>();
      int _minLength = strs[0].length();
       for (String s: strs) {
           chars.add(s.toCharArray());
          if (_minLength > s.length()) {
                _minLength = s.length();
         }
        }

       List<Character> result = new ArrayList<>();
      boolean breaked = false;
     for (int i = 0; i < _minLength; i++) {
            char ch1 = chars.get(0)[i];
          for (int j = 1; j < strs.length; j++) {
               if (chars.get(j)[i] != ch1) {
                    breaked = true;
                  break;
               }
            }
            if (breaked) {
               break;
           }
            result.add(ch1);
     }

       if (result.size() == 0) {
            return "";
       } else {
         StringBuilder sb = new StringBuilder();
          for (Character character: result) {
              sb.append(character);
            }
            return sb.toString();
        }
    }
}

class Solution {
   public boolean isValid(String s) {
        char[] chars = s.toCharArray();

       if (chars.length == 0 ) {
           return true;
       }

       if (chars.length < 2 || chars.length % 2 != 0) {
           return false;
       }

        char[] stack = new char[chars.length];
        int j = 0;
        stack[0] = chars[0];
        for (int i = 1; i < chars.length; i++) {
            if (j >= 0 && (stack[j] == '('  && chars[i] == ')'
                    || stack[j] == '[' && chars[i] == ']'
                    || stack[j] == '{' && chars[i] == '}') ) {
                j--;
            } else {
                stack[j+1] = chars[i];
                j = j + 1;
            }
        }

        if (j == -1) {
            return true;
        }

        return false;
    }
}