Java反转字符串
- 编写一个函数，其作用是将输入的字符串反转过来。输入字符串以字符数组 s 的形式给出。
- 不要给另外的数组分配额外的空间，你必须原地修改输入数组、使用 O(1) 的额外空间解决这一问题。
public void reverseString(char[] s) {
for (int i = 0; i < s.length/2; i++) {
char right = s[s.length - (i + 1)];
char left = s[i];
s[i] = right;
s[s.length - (i + 1)] = left;
}
}
整数反转
- 给你一个 32 位的有符号整数 x ，返回将 x 中的数字部分反转后的结果。
public int reverse(int x) {
boolean isTrue = true;
if (x < 0){
isTrue = false;
x = Math.abs(x);
}
String num = "";
ArrayList<Character> characterArrayList = new ArrayList<>();
for (int i = 0; i < String.valueOf(x).length(); i++) {
characterArrayList.add(String.valueOf(x).charAt(i));
}
for (int i = 0; i < characterArrayList.size(); i++) {
num += characterArrayList.get(characterArrayList.size() - (i + 1));
}
int i = Integer.parseInt(num);
if (isTrue == false){
i = i - (i*2);
}
return i;
}
Java返回字符串中的第一个唯一字符
- 给定一个字符串，找到它的第一个不重复的字符，并返回它的索引。如果不存在，则返回 -1。
public int firstUniqChar(String s) {
for (int i = 0; i < s.length(); i++) {
if (s.indexOf(s.charAt(i)) == s.lastIndexOf(s.charAt(i))){
return i;
}
}
return -1;
}
也可以用两次遍历来判定.不过时间会比较长
这个就是看该字符的第一个位置和最后一个位置是否相同来进行判断的
Java判断有效的字母异位词
- 给定两个字符串 s 和 t ，编写一个函数来判断 t 是否是 s 的字母异位词。
public boolean isAnagram(String s, String t) {
ArrayList<String> stringArrayListFirst = new ArrayList<>();
ArrayList<String> stringArrayListSecond = new ArrayList<>();
for (int i = 0; i < s.length(); i++) {
stringArrayListFirst.add(String.valueOf(s.charAt(i)));
}
for (int i = 0; i < t.length(); i++) {
stringArrayListSecond.add(String.valueOf(t.charAt(i)));
}
for (int i = 0; i < t.length(); i++) {
stringArrayListFirst.remove(t.substring(i, i + 1));
}
for (int i = 0; i < s.length(); i++) {
stringArrayListSecond.remove(s.substring(i, i + 1));
}
if (stringArrayListFirst.size()+ stringArrayListSecond.size() == 0){
return true;
}
return false;
}
代码过于臃肿.看了下评论区可以排序后直接比较.....人家才四行代码
Java验证回文串
- 给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。
public boolean isPalindrome(String s) {
String a = "";
for (int i = 0; i < s.length(); i++) {
if (Character.isLetterOrDigit(s.charAt(i))){
a += s.charAt(i);
}
}
a = a.toLowerCase();
for (int i = 0; i < a.length()/2; i++) {
if (a.charAt(i) != a.charAt(a.length()-(i+1))){
return false;
}
}
return true;
}
可以考虑处理完特殊字符后对半切然后把后半部分反转再直接比较可能更快些
字符串转换整数 (atoi)
- 请你来实现一个 myAtoi(string s) 函数，使其能将字符串转换成一个 32 位有符号整数（类似 C/C++ 中的 atoi 函数）。
这个我写了一个半小时放弃了…来看看半成品代码
public int myAtoi(String s) {
String a = "";
boolean is = false;
if (s.length() == 0 || s.equals("-")){
return 0;
}
for (int i = 0; i < s.trim().length(); i++) {
if (s.trim().charAt(0) == '-'){
is = true;
if (Character.isDigit(s.trim().charAt(i))){
a += s.trim().charAt(i);
}else if (i == 0){
continue;
}else {
continue;
}
}else {
if (!Character.isDigit(s.trim().charAt(0))){
System.out.println("0");
}else if(s.trim().charAt(0) == '+'){
continue;
}else {
if (Character.isDigit(s.trim().charAt(i))){
a += s.trim().charAt(i);
}else {
continue;
}
}
}
}
int b = 0;
if (a.length() == 0){
return 0;
}
try{
if (is == true){
b = Integer.parseInt(a) - Integer.parseInt(a)*2;
return b;
}else {
b = Integer.parseInt(a);
return b;
}
}catch (Exception e){
if (is == true){
return Integer.MIN_VALUE;
}
return Integer.MAX_VALUE;
}
}
实现 strStr()
- 给你两个字符串 haystack 和 needle ，请你在 haystack 字符串中找出 needle 字符串出现的第一个位置（下标从 0 开始）。如果不存在则返回 -1 。
这题很迷啊.我也不想多说啥了
public int strStr(String haystack, String needle) {
if (needle.length() == 0){
return 0;
}
if (haystack.length() == 0){
return -1;
}
for (int i = 0; i < haystack.length(); i++) {
if (haystack.charAt(i) == needle.charAt(0)){
System.out.println(i);
return i;
}
}
return -1;
}
代码明明没啥问题就不给我过....有没有大牛来给我看看咋回事
外观数列
- 给定一个正整数 n ，输出外观数列的第 n 项。
- 「外观数列」是一个整数序列，从数字 1 开始，序列中的每一项都是对前一项的描述。
好嘛根本不会做看看大佬的写法hahahhahaha
class Solution {
public String countAndSay(int n) {
switch (n){
case 1: return "1";
case 2: return "11";
case 3: return "21";
case 4: return "1211";
case 5: return "111221";
case 6: return "312211";
case 7: return "13112221";
case 8: return "1113213211";
case 9: return "31131211131221";
case 10: return "13211311123113112211";
case 11: return "11131221133112132113212221";
case 12: return "3113112221232112111312211312113211";
case 13: return "1321132132111213122112311311222113111221131221";
case 14: return "11131221131211131231121113112221121321132132211331222113112211";
case 15: return "311311222113111231131112132112311321322112111312211312111322212311322113212221";
case 16: return "132113213221133112132113311211131221121321131211132221123113112221131112311332111213211322211312113211";
case 17: return "11131221131211132221232112111312212321123113112221121113122113111231133221121321132132211331121321231231121113122113322113111221131221";
case 18: return "31131122211311123113321112131221123113112211121312211213211321322112311311222113311213212322211211131221131211132221232112111312111213111213211231131122212322211331222113112211";
case 19: return "1321132132211331121321231231121113112221121321132122311211131122211211131221131211132221121321132132212321121113121112133221123113112221131112311332111213122112311311123112111331121113122112132113213211121332212311322113212221";
case 20: return "11131221131211132221232112111312111213111213211231132132211211131221131211221321123113213221123113112221131112311332211211131221131211132211121312211231131112311211232221121321132132211331121321231231121113112221121321133112132112312321123113112221121113122113121113123112112322111213211322211312113211";
case 21: return "311311222113111231133211121312211231131112311211133112111312211213211312111322211231131122211311122122111312211213211312111322211213211321322113311213212322211231131122211311123113223112111311222112132113311213211221121332211211131221131211132221232112111312111213111213211231132132211211131221232112111312211213111213122112132113213221123113112221131112311311121321122112132231121113122113322113111221131221";
case 22: return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
case 23: return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
case 24: return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
case 25: return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
case 26: return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
case 27: return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
case 28: return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
case 29: return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
case 30: return "3113112221131112311332111213122112311311123112111331121113122112132113121113222112311311221112131221123113112221121113311211131122211211131221131211132221121321132132212321121113121112133221123113112221131112212211131221121321131211132221123113112221131112311332211211133112111311222112111312211311123113322112111312211312111322212321121113121112133221121321132132211331121321132213211231132132211211131221232112111312212221121123222112311311222113111231133211121321321122111312211312111322211213211321322123211211131211121332211231131122211311123113321112131221123113111231121123222112111331121113112221121113122113111231133221121113122113121113221112131221123113111231121123222112111312211312111322212321121113121112131112132112311321322112111312212321121113122122211211232221121321132132211331121321231231121113112221121321132132211322132113213221123113112221133112132123222112111312211312112213211231132132211211131221131211322113321132211221121332211231131122211311123113321112131221123113111231121113311211131221121321131211132221123113112211121312211231131122211211133112111311222112111312211312111322211213211321223112111311222112132113213221133122211311221122111312211312111322212321121113121112131112132112311321322112111312212321121113122122211211232221121321132132211331121321231231121113112221121321132132211322132113213221123113112221133112132123222112111312211312112213211231132132211211131221131211322113321132211221121332211213211321322113311213212312311211131122211213211331121321123123211231131122211211131221131112311332211213211321223112111311222112132113213221123123211231132132211231131122211311123113322112111312211312111322111213122112311311123112112322211213211321322113312211223113112221121113122113111231133221121321132132211331222113321112131122211332113221122112133221123113112221131112311332111213122112311311123112111331121113122112132113121113222112311311221112131221123113112221121113311211131122211211131221131211132221121321132132212321121113121112133221123113112221131112311332111213122112311311123112112322211322311311222113111231133211121312211231131112311211232221121113122113121113222123211211131221132211131221121321131211132221123113112211121312211231131122113221122112133221121321132132211331121321231231121113121113122122311311222113111231133221121113122113121113221112131221123113111231121123222112132113213221133112132123123112111312211322311211133112111312211213211311123113223112111321322123122113222122211211232221121113122113121113222123211211131211121311121321123113213221121113122123211211131221121311121312211213211321322112311311222113311213212322211211131221131211221321123113213221121113122113121113222112131112131221121321131211132221121321132132211331121321232221123113112221131112311322311211131122211213211331121321122112133221121113122113121113222123112221221321132132211231131122211331121321232221121113122113121113222123211211131211121332211213111213122112132113121113222112132113213221232112111312111213322112132113213221133112132123123112111311222112132113311213211221121332211231131122211311123113321112131221123113112221132231131122211211131221131112311332211213211321223112111311222112132113212221132221222112112322211211131221131211132221232112111312111213111213211231131112311311221122132113213221133112132123222112311311222113111231132231121113112221121321133112132112211213322112111312211312111322212321121113121112131112132112311321322112111312212321121113122122211211232221121311121312211213211312111322211213211321322123211211131211121332211213211321322113311213211322132112311321322112111312212321121113122122211211232221121321132132211331121321231231121113112221121321133112132112312321123113112221121113122113111231133221121321132122311211131122211213211321222113222122211211232221123113112221131112311332111213122112311311123112111331121113122112132113121113222112311311221112131221123113112221121113311211131122211211131221131211132221121321132132212321121113121112133221123113112221131112311332111213213211221113122113121113222112132113213221232112111312111213322112132113213221133112132123123112111312211322311211133112111312212221121123222112132113213221133112132123222113223113112221131112311332111213122112311311123112112322211211131221131211132221232112111312111213111213211231132132211211131221131211221321123113213221123113112221131112211322212322211231131122211322111312211312111322211213211321322113311213211331121113122122211211132213211231131122212322211331222113112211";
}
return null;
}
}
作者：Cany
链接：https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnpvdm/?discussion=yAWCtQ
来源：力扣（LeetCode）
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
最长公共前缀
- 编写一个函数来查找字符串数组中的最长公共前缀。
- 如果不存在公共前缀，返回空字符串 “”。
emmmm还是不会做…看看半成品吧~
public String longestCommonPrefix(String[] strs) {
if (strs.length == 1){
return strs[0];
}
String pre = "";
Integer minLength = 0;
for (int i = 0; i < strs.length; i++) {
if (strs[i].length() < strs[minLength].length()){
minLength = i;
}
}
String s = strs[minLength];
for (int i = 0; i < s.length(); i++) {
String substring = s.substring(0, s.length() - i);
for (int j = 0; j < strs.length; j++) {
if (!strs[j].contains(substring)){
pre = substring;
}
}
}
return pre.substring(0,pre.length()-1);
}
再来看看人家的写法
public String longestCommonPrefix(String[] strs) {
// 找出最小长度的的字符串
int minLen = Integer.MAX_VALUE;
String minStr = "";
for (String str : strs) {
if (minLen > str.length()) {
minLen = str.length();
minStr = str;
}
}
for (String str : strs) {
while (minLen > 0) {
// 是否是共同前缀
boolean start = str.startsWith(minStr.substring(0, minLen));
if (start) {
break;
} else {
minLen--;
}
}
}
return minStr.substring(0, minLen);
}
作者：FD_LeetCode
链接：https://leetcode-cn.com/leetbook/read/top-interview-questions-easy/xnmav1/?discussion=RTNpup
来源：力扣（LeetCode）
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。