继续在力扣网用java练题。主要作为自己的笔记吧，后面再把算法运行速度优化下。
下面是题目链接： 力扣网 探索初级算法 字符串 跳转链接
字符串
反转字符串 public static void reverseString(char[] s) { int len=s.length; for (int i = 0; i < len/2; i++) { char a=s[len-i-1]; s[len-i-1]=s[i]; s[i]=a; } } 整数反转 public static int reverse(int x) { Long num=0L; int symbol=0; //保存符号 if(x<0){ symbol=1; x*=-1; } while (x>0){ int a=x; num=num*10+a; x=x/10; } //加上符号 num=symbol==0?num:num*-1; if(num>Integer.MIN_VALUE&&num< Integer.MAX_VALUE){ return num.intValue(); } return 0; } 字符串中的第一个唯一字符 public int firstUniqChar(String s) { char[] str=s.toCharArray(); for (int i = 0; i <str.length ; i++) { int same=0; for (int j = 0; j < str.length; j++) { if(str[i]==str[j]&&i!=j){ same=1; j=str.length; } } if(same==0){ return i; } } return -1; } 有效的字母异位词 public boolean isAnagram(String s, String t) { if(s.length()!=t.length()){ return false; } StringBuffer strs=new StringBuffer(); StringBuffer strt=new StringBuffer(); for (char i = 'a'; i < 'z'; i++) { for (int j = 0; j < s.length(); j++) { if (i==s.charAt(j)){ strs.append(i); } } for (int j = 0; j < t.length(); j++) { if (i==t.charAt(j)){ strt.append(i); } } } if (strs.toString().equals(strt.toString())){ return true; }else { return false; } } 验证回文字符串 public boolean isPalindrome(String s) { s=s.trim(); return huiwen(s,0,s.length()-1,false); } public static boolean huiwen(String s,int start,int end,Boolean has){ Boolean bStart=false; Boolean bEnd=false; while (!bStart||!bEnd){ if(start>=end){ return true; } char startC=s.charAt(start); bStart= ('a'<=startC&&startC<='z')||('A'<=startC&&startC<='Z'||'0'<=startC&&startC<='9'); char endC=s.charAt(end); bEnd=('a'<=endC&&endC<='z')||('A'<=endC&&endC<='Z'||'0'<=endC&&endC<='9'); if(!bStart){ start+=1; } if(!bEnd){ end-=1; } } if(!String.valueOf(s.charAt(start)).equalsIgnoreCase(String.valueOf(s.charAt(end)))){ return false; } return huiwen(s,start+1,end-1,true); } 字符串转换整数 (atoi) public int myAtoi(String str) { str=str.trim(); int symbol=0; //0 无符号 1='-' 2='+' int start=0; int size=0; if(str.length()>0){ int index=0; if(str.charAt(0)=='-'){ symbol=1; index++; }else if(str.charAt(0)=='+'){ symbol=2; index++; } for (int i = index; i <str.length() ; i++) { if(str.charAt(i)>='0'&&str.charAt(i)<='9'){ if(str.charAt(i)=='0'&&size==0){ start+=1; }else { size+=1; } }else { break; } } String s=str.substring(symbol==0?start:start+1,symbol==0?start+size:start+size+1); if(s.length()<=0){ return 0; } if(s.length()>10){ return symbol==1?Integer.MIN_VALUE:Integer.MAX_VALUE; }else { Long num=symbol==1?Long.parseLong(s)*-1:Long.parseLong(s); if(num>Integer.MIN_VALUE&&num<Integer.MAX_VALUE){ return num.intValue(); } return symbol==1?Integer.MIN_VALUE:Integer.MAX_VALUE; } } return 0; } 实现strStr() public int strStr(String haystack, String needle) { if (haystack.contains(needle)){ String newHayStack=haystack.replace(needle,"-"); return newHayStack.indexOf("-"); } return -1; } 报数 public String countAndSay(int n) { if(n==1){ return "1"; } String count=countAndSay(n-1); StringBuffer s=new StringBuffer(); for (int i = 0; i <count.length() ;) { int num=1; for (int j = i+1; j < count.length(); j++) { if(count.charAt(i)==count.charAt(j)){ num++; }else { break; } } s.append(num); s.append(count.charAt(i)); i+=num; } return s.toString(); } 最长公共前缀 public String longestCommonPrefix(String[] strs) { if(strs.length==0){ return ""; }else if(strs.length==1){ return strs[0]; } String same=""; same=strs[0]; for (int i = 1; i <strs.length ; i++) { int size=0; for (int j = 0; j < strs[i].length(); j++) { if(j<same.length()&&same.charAt(j)==strs[i].charAt(j)){ size++; }else { break; } } same=same.substring(0,size); } return same; }