算法奇妙屋(七)-字符串操作

    public String longestCommonPrefix(String[] strs) {
        StringBuilder ret = new StringBuilder();
        ret.append(strs[0]);
        int j = 0;
        for (int i = 1; i < strs.length; i++) {
            j = 0;
            while (j < ret.length() && j < strs[i].length()) {
                if (ret.charAt(j) == strs[i].charAt(j)) {
                    if (j >= ret.length()) {
                        ret.append(strs[i].charAt(j));
                    }
                }else {
                    break;
                }
                j++;
            }
            if (j < ret.length()) {
                ret.delete(j, ret.length()); // 删除多余不相同的字符
            }
        }
        return ret.toString();
    }

    public String longestCommonPrefix(String[] strs) {
        int i = 0;
        while(i < strs[0].length()) {
            char ch = strs[0].charAt(i);
            for (int j = 1; j < strs.length; j++) {
                if (i >= strs[j].length() || ch != strs[j].charAt(i)) {
                    return strs[0].substring(0,i);
                }
            }
            i++;
        }
        return strs[0];
    }

    public String longestPalindrome(String s) {
        int len = 0;
        int start = 0;
        int left = 0;
        int right = 0;
        for (int i = 0; i < s.length(); i++) {
            left = i - 1;
            right = i + 1;
            while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
                left--;
                right++;
            }
            if ((right - left - 1) > len) {
                len = right - left - 1;
                start = left + 1;
            }
            left = i;
            right = i + 1;
            while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
                left--;
                right++;
            }
            if ((right - left - 1) > len) {
                len = right - left - 1;
                start = left + 1;
            }
        }
        return s.substring(start,start + len);
    }

    public String addBinary(String a, String b) {
        int cur1 = a.length() - 1;
        int cur2 = b.length() - 1;
        char[] ch1 = a.toCharArray();
        char[] ch2 = b.toCharArray();
        int tmp = 0;
        StringBuilder ret = new StringBuilder();
        while(cur1 >= 0 || cur2 >= 0 || tmp != 0) {
            if (cur1 >= 0) {
                tmp += a.charAt(cur1) - '0';
                cur1--;
            }
            if (cur2 >= 0) {
                tmp += b.charAt(cur2) - '0';
                cur2--;
            }
            ret.append(tmp % 2);
            tmp /= 2;
        }
        ret.reverse();
        return ret.toString();
    }

    public String multiply(String num1, String num2) {
        StringBuilder ss1 = new StringBuilder(num1);
        ss1.reverse();
        String s1 = ss1.toString();
        StringBuilder ss2 = new StringBuilder(num2);
        ss2.reverse();
        String s2 = ss2.toString();
        if (s1.equals("0") || s2.equals("0")) {
            return "0";
        }
        int m = num1.length();
        int n = num2.length();
        int[] tmp = new int[m + n - 1];
        for (int i = 0; i < m; i++) {
            for (int j = 0; j < n; j++) {
                tmp[i + j] += ((s1.charAt(i) - '0') * (s2.charAt(j) - '0'));
            }
        }
        int t = 0;
        int i = 0;
        StringBuilder ret = new StringBuilder();
        while (i < tmp.length || t != 0) {
            if (i < m + n - 1) {
                t += tmp[i];  
            }
            ret.append(t % 10);
            t /= 10;
            i++;
        }
        ret.reverse();
        return ret.toString();
    }