2011.04.22——— 星期三的面试题
今天面试去了 把几道面试题 记一下吧
1、实现把一个整数字符串转换为整数
看一下Integer.parsentInt()
/** * Parses the string argument as a signed integer in the radix * specified by the second argument. The characters in the string * must all be digits of the specified radix (as determined by * whether {@link java.lang.Character#digit(char, int)} returns a * nonnegative value), except that the first character may be an * ASCII minus sign <code>'-'</code> (<code>'\u002D'</code>) to * indicate a negative value. The resulting integer value is returned. * <p> * An exception of type <code>NumberFormatException</code> is * thrown if any of the following situations occurs: * <ul> * <li>The first argument is <code>null</code> or is a string of * length zero. * <li>The radix is either smaller than * {@link java.lang.Character#MIN_RADIX} or * larger than {@link java.lang.Character#MAX_RADIX}. * <li>Any character of the string is not a digit of the specified * radix, except that the first character may be a minus sign * <code>'-'</code> (<code>'\u002D'</code>) provided that the * string is longer than length 1. * <li>The value represented by the string is not a value of type * <code>int</code>. * </ul><p> * Examples: * <blockquote><pre> * parseInt("0", 10) returns 0 * parseInt("473", 10) returns 473 * parseInt("-0", 10) returns 0 * parseInt("-FF", 16) returns -255 * parseInt("1100110", 2) returns 102 * parseInt("2147483647", 10) returns 2147483647 * parseInt("-2147483648", 10) returns -2147483648 * parseInt("2147483648", 10) throws a NumberFormatException * parseInt("99", 8) throws a NumberFormatException * parseInt("Kona", 10) throws a NumberFormatException * parseInt("Kona", 27) returns 411787 * </pre></blockquote> * * @param s the <code>String</code> containing the integer * representation to be parsed * @param radix the radix to be used while parsing <code>s</code>. * @return the integer represented by the string argument in the * specified radix. * @exception NumberFormatException if the <code>String</code> * does not contain a parsable <code>int</code>. */ public static int parseInt(String s, int radix)throws NumberFormatException { if (s == null) { throw new NumberFormatException("null"); }if (radix < Character.MIN_RADIX) { throw new NumberFormatException("radix " + radix + " less than Character.MIN_RADIX");}if (radix > Character.MAX_RADIX) { throw new NumberFormatException("radix " + radix + " greater than Character.MAX_RADIX");}int result = 0;boolean negative = false;int i = 0, max = s.length();int limit;int multmin;int digit;if (max > 0) { if (s.charAt(0) == '-') {negative = true;limit = Integer.MIN_VALUE;i++; } else {limit = -Integer.MAX_VALUE; } multmin = limit / radix; if (i < max) {digit = Character.digit(s.charAt(i++),radix);if (digit < 0) { throw NumberFormatException.forInputString(s);} else { result = -digit;} } while (i < max) {// Accumulating negatively avoids surprises near MAX_VALUEdigit = Character.digit(s.charAt(i++),radix);if (digit < 0) { throw NumberFormatException.forInputString(s);}if (result < multmin) { throw NumberFormatException.forInputString(s);}result *= radix;if (result < limit + digit) { throw NumberFormatException.forInputString(s);}result -= digit; }} else { throw NumberFormatException.forInputString(s);}if (negative) { if (i > 1) {return result; } else {/* Only got "-" */throw NumberFormatException.forInputString(s); }} else { return -result;} }2、找出两个数组中相同项
3、二分法 有返回 1 没有返回-1
先排序。。
int[] arrays = new int[]{1,2,3,4,5,6};int find = 4;int result = -1;int start = 0;int end = arrays.length-1;int index = 0while(true){index = (start+end)/2;if(find > arrays[index]){start = index+1;}else if(find < arrays[index]){end = index-1;}else{result = 1;break;}}4、单向链表 反向输出 输入 a->c->b->e 输出e->b->c->a
参考：http://article.yeeyan.org/view/9225/173996
http://apps.hi.baidu.com/share/detail/30195452
5、字符串中重复最多的字母及其次数
答案竟然是用map，key为字母 value为次数
6、sql
参考：http://blog.csdn.net/ccsuliuxing/archive/2007/04/18/1568821.aspx
http://topic.csdn.net/u/20110110/09/32a1e6ad-c619-4f1f-b79a-b2a226af56bc.html
表A(id number(10),name varchar2(10),regdate date)用户ID,用户姓名,注册时间.
表B(id number(10),groupid varchar2(10))用户ID,用户分组组号
表A(id number(10),name varchar2(10))用户ID,用户姓名
写出下面的SQL语句
1.统计A表中每个月注册用户数
2.统计A表中有姓名相同的用户数
3.如果表A中有姓名相同的用户,把相同的查出,写入表C中
4.A中ID有多个相同的数据,A中姓名相同的ID只保留注册时间最大的数据
1 select count(*),to_char(regdate, 'yyyymm ') from A group by to_char(regdate, 'yyyymm '); 2 select count(*) from (select name from A group by name having count(*) > 1); 3 insert into C(name2) select name from A group by name having count(*) > 1; 4 delete from A E where e.regdate < (select max(regdate) from a X where E.id = X.id);