<一>替换空格
public class Solution {
public String replaceSpace(StringBuffer str) {
int len = str.length();
StringBuffer res = new StringBuffer();
for(int i = 0;i < len;i++){
if(str.charAt(i) != ‘ ‘){
res.append(str.charAt(i));
}else{
res.append("%20");
}
}
return res.toString();
}
<二>正则表达式匹配
public class Solution {
public boolean match(char[] str, char[] pattern) {
if((null == str && null == pattern) || (null != str && pattern == null)){
return true;
}
if(null == str && pattern != null){
return false;
}
return modeoMatch(str,pattern,0,0);
}
private boolean modeoMatch(char[] str,char[] pattern,int slen,int plen){
if(slen == str.length && plen == pattern.length){
return true;
}
if(slen != str.length && plen == pattern.length){
return false;
}
if(plen + 1 < pattern.length && pattern[plen + 1] == ‘*‘){
if(slen < str.length && (str[slen] == pattern[plen] || pattern[plen] == ‘.‘)){
return modeoMatch(str,pattern,slen + 1,plen) || modeoMatch(str,pattern,slen,plen + 2);
}else{
return modeoMatch(str,pattern,slen,plen + 2);
}
}
//必须放在后面，因为从后面的先判断才对
if(slen < str.length && (str[slen] == pattern[plen] || pattern[plen] == ‘.‘)){
return modeoMatch(str,pattern,slen + 1,plen + 1);
}
return false;
}
}
<三>表示数值的字符串
public class Solution {
private int index = 0;
public boolean isNumeric(char[] str) {
if(str.length <= 0){
return false;
}
boolean flag = scanInteger(str);
if(index < str.length && str[index] == ‘.‘){
index++;
flag = scanInteger(str) || flag;
}
if(index < str.length && (str[index] == ‘E‘ || str[index] == ‘e‘)){
index++;
flag = flag && scanInteger(str);
}
return flag && index == str.length;
}
private Boolean scanInteger(char[] str){ //加减符号后面该出现的
if(index < str.length && (str[index] == ‘+‘ || str[index] == ‘-‘)){
index++;
}
int start = index;
//Character.isDigit(str[index]) 相同与 str[index] >= ‘0‘ && str[index] <= ‘9‘
while(index < str.length && str[index] >= ‘0‘ && str[index] <= ‘9‘){
index++;
}
return start < index;
}
}
<四>字符流中第一个不重复的字符
如果当前字符流没有存在出现一次的字符，返回#字符。
代码如下：
import java.util.HashMap;
import java.util.ArrayList;
public class Solution {
HashMap<Character,Integer> map = new HashMap<Character,Integer>();
ArrayList list = new ArrayList();
//Insert one char from stringstream
public void Insert(char ch) {
if(!map.containsKey(ch)){
map.put(ch,1);
list.add(ch);
}else{
map.put(ch,map.get(ch) + 1);
}
}
//return the first appearence once char in current stringstream
public char FirstAppearingOnce() {
for(int i = 0;i < list.size();i++){
if(map.get(list.get(i)) == 1){
return (char)list.get(i);
}
}
return ‘#‘;
}
}
原文：https://www.cnblogs.com/youdiaodaxue16/p/11374567.html