I'd like to know if there's any Dart function like PHP's strrev(). If not, could you please show my any source code how to make it on my own?
Thank you.
Lists can be reversed, so you can use this to reverse a String as well:
new String.fromCharCodes("input".charCodes.reversed.toList());
I haven't found one in the API, as a brand new Dart user (as of this afternoon). However, reversing a string is pretty easy to do in any language. Here's the typical O(n) solution in Dart form:
String reverse(String s) {
var chars = s.splitChars();
var len = s.length - 1;
var i = 0;
while (i < len) {
var tmp = chars[i];
chars[i] = chars[len];
chars[len] = tmp;
i++;
len--;
}
return Strings.concatAll(chars);
}
void main() {
var s = "dog";
print(s);
print(reverse(s));
}
May be a standardized reverse() method will be implemented in future in List (dart issue 2804), the following is about 8 to 10 times faster than the previous typical solution:
String reverse(String s) {
// null or empty
if (s == null|| s.length == 0)
return s;
List<int> charCodes = new List<int>();
for (int i = s.length-1; i>= 0; i-- )
charCodes.addLast(s.charCodeAt(i)) ;
return new String.fromCharCodes(charCodes);
}
try this instead of others.
String try(str) {
return str.split('').reversed.join('');
}
String theString = "reverse the string";
List<String> reslt = theString.split("");
List<String> reversedString = List.from(reslt.reversed);
String joinString = reversedString.join("");
print(joinString);
Ouput: gnirts eht esrever
Related
I'm getting an error in this code:
void main() {
List<String> wave(String str) {
List<String> results = [];
String newStr;
int i = 0;
for (String ltr in str.split('')) {
newStr = str;
if (ltr != ' ') {
newStr[i] = ltr.toUpperCase();
results.add(newStr);
}
i++;
}
return results;
}
print(wave(' gap '));
}
the error is at the line:
newStr[i] = ltr.toUpperCase;
Despite when I try print(newStr[i]); I don't get an error and the code is executed correctly!
In Dart String operation, operator[] returns a string. Which means, array[index] is used for getting the string in the index position. That is why you're getting that error, because you can't set at specific index using this operator[] in dart. See the documentation for details.
To replace at the specific index in dart, you can use replaceFirst(Pattern from, String to, [int startIndex = 0]) as the other answer mentioned. Or, you can use substring(int start, [int? end]) as follows:
if (ltr != ' ' && i < newStr.length) {
newStr = newStr.substring(0, i) + ltr.toUpperCase() + newStr.substring(i+1);
results.add(newStr);
}
To make the code bug free, I've added the checking of the value of i in it. You should add the checking to avoid out of bound access.
try to replace
newStr[i] = ltr.toUpperCase();
to
newStr = newStr.replaceFirst(ltr,ltr.toUpperCase(),i);
So the result will be [ Gap , gAp , gaP ]
Honestly, I don't know how char is defined in Dart, but I think accessing index of String is kind of getter, thus cannot be set to a new value.
I have a simple exercise in Coderbyte, it just want to have a function that's WordSplit(strArr) read the array of strings stored in strArr, For example I have two elements like ["hellocat", "apple,bat,cat,goodbye,hello,yellow,why"]
I just want to to determine if the first element in the input can be split into two words, where both words exist in the dictionary that is provided in the second input.
For example: the first element can be split into two words: hello and cat because both of those words are in the dictionary.
So the program should return the two words that exist in the dictionary separated by a comma, as this result hello,cat .
I've made a recursive solution below. It checks if the string to be split starts with any word in the dictionary. If it exists, the function is called again using a substring with that first word removed.
This function only works up to the first word that isn't in the dictionary since you did not specify the expected behavior when the inputted word is not made up of words in the dictionary. You could make it throw an exception perhaps, but please specify your expectation.
void main() {
print(wordSplit(["hellocat", "apple,bat,cat,goodbye,hello,yellow,why"]));
//hello,cat
}
String wordSplit(List<String> arg) {
String wordToSplit = arg[0];
String dict = arg[1];
List<String> parsedDict = arg[1].split(',');
for(String word in parsedDict) {
if(wordToSplit.startsWith(word)) {
//If the substring would be empty, don't do more recursion
if(word.length == wordToSplit.length) {
return word;
}
return word + ',' + wordSplit([wordToSplit.substring(word.length), dict]);
}
}
return wordToSplit;
}
#include <bits/stdc++.h>
using namespace std;
vector<string> converToWords(string dict) {
vector<string> res;
string s = "";
int n = dict.length();
for(int i=0; i<n; i++) {
if(dict[i] == ',') {
res.push_back(s);
s = "";
}
else s += dict[i];
}
res.push_back(s);
s = "";
return res;
}
string solve(string str[]) {
string result = "";
string word = str[0], dict = str[1];
int n = word.length();
vector<string> vs = converToWords(dict);
unordered_set<string> ust;
for(auto it: vs) ust.insert(it);
// for(auto i=ust.begin(); i!=ust.end(); i++){
// cout<<*i<<endl;
// }
string s = "";
for(int i=0; i<n; i++) {
s += word[i];
// cout<<s<<endl;
string temp = word.substr(i+1, n-(i+1));
// cout<<temp<<endl;
if(ust.find(s) != ust.end() && ust.find(temp) != ust.end()) {
cout<<s<<endl;
cout<<temp<<endl;
result += s+","+temp;
break;
}
temp = "";
}
return result;
}
int main() {
string arr[2];
cin>>arr[0]>>arr[1];
cout << solve(arr);
return 0;
}
I'm trying to convert strings to arrays then compare two arrays. If the same value needs to remove from both array. Then finally merge two arrays and find array length. Below is my code
String first_name = "siva";
String second_name = "lovee";
List<String> firstnameArray=new List();
List<String> secondnameArray=new List();
firstnameArray = first_name.split('');
secondnameArray = second_name.split('');
var totalcount=0;
for (int i = 0; i < first_name.length; i++) {
for (int j = 0; j < second_name.length; j++) {
if (firstnameArray[i] == secondnameArray[j]) {
print(firstnameArray[i] + "" + " == " + secondnameArray[j]);
firstnameArray.removeAt(i);
secondnameArray.removeAt(i);
break;
}
}
}
var finalList = new List.from(firstnameArray)..addAll(secondnameArray);
print(finalList);
print(finalList.length);
But always getting this error Unsupported operation: Cannot remove from a fixed-length list can you help me how to fix this issue. Thanks.
Seems like what you are trying to do is to find the length of unique characters in given two strings. Well, the Set type is perfect for this use-case. Here's an example of what you can do:
void main() {
String first = 'abigail';
String second = 'allie';
var unique = '$first$second'.split('').toSet();
print(unique);
}
This would give you an output of:
{a, b, i, g, l, e}
On which you may perform functions like .toList(), or .where() or .length.
You can ensure that firstnameArray, secondnameArray is not a fixed-length list by initializing it as below:
var firstnameArray = new List<String>.from(first_name.split(''));
var secondnameArray= new List<String>.from(second_name.split(''));
Thereby declaring firstnameArray, secondnameArray to be a mutable copy of input.
I'm stuck on this common interview question using Dart. I need to return the most common character in a given string. I'm trying to create a map with a count for each character as the first step.
This is my progress so far:
main(List<String> arguments) {
maxChar('hello');
}
void maxChar(String word) {
Map<String, int> charMap = {};
int max = 0;
String maxChar = '';
word.split('').forEach((char) {
if(charMap.containsValue(char)) {
charMap[char]+1;
return;
} else {
charMap[char] = 1;
}
});
print(charMap);
}
Right now its not even counting the correct amount of the letter 'l'. It's outputting:
{h: 1, e: 1, l: 1, o: 1}
What am I doing wrong? Is there an easier way to return the most common character in a String in Dart?
Thanks!
EDIT:
Ok, I've solved it, but surely there is a more concise way of solving this problem. See my solution below:
main(List<String> arguments) {
print(max_char.maxChar('hello'));
}
String maxChar(String word) {
Map<String, int> charMap = {};
int max = -1;
String maxChar = '';
word.split('').forEach((char) {
if(charMap.containsKey(char)) {
charMap[char]++;
return;
} else {
charMap[char] = 1;
}
});
charMap.forEach((k,v) {
if(v > max) {
max = v;
maxChar = k;
}
});
return maxChar;
}
A shorter approach to counting the characters is definitely possible:
String charCount(String chars) {
int maxChar = -1;
int maxCount = 0;
var counts = <int, int>{};
for (var char in chars.runes) {
int count = counts.update(char, (n) => n + 1, ifAbsent: () => 1);
if (count > maxCount) {
maxCount = count;
maxChar = char;
}
}
return String.fromCharCode(maxChar);
}
If you just want to count the characters, you can remove all the lines mentioning maxCount and maxChar.
I use integers to represent the characters instead of strings. That's cheaper and just as precise, and it allows you to recognize and combine Unicode UTF-16 surrogates.
An array of Image Url path:
["http://cdncms.fonts.net/hero-images/FEX_Hero_Thumb.png ","http://cdncms.fonts.net/hero-images/Wilma_Hero_Thumb.png "]
asp.net mvc Controller :
public ActionResult Extract(string[] name)
{
//List<string> myList = name.ToList<string>();
for(int x = 0; x < name.Length; x++)
{
//string something = name[x];
var item = name[x];
Session["values"] = item;
}
char[] delimiter1 = new char[] { ',' }; // <-- Split on these
string[] array1 = Session["values"].ToString().Split(delimiter1, StringSplitOptions.RemoveEmptyEntries);
foreach (var item in array1)
{
string exts = Path.GetExtension(item); //illegal character
string strRealname = Path.GetFileName(item); illegal character
}
I know this problem due to the presence of [ character at the beginning and last .I have tried but not succeeded .Any idea how to remove this using split function in C#
Assuming that you have correctly identified the problem, you could do this before making it an array:
var values = Session["values"].ToString();
if(values.StartsWith("[")) values = values.Substring(1);
if(values.EndsWith("]")) values = values.Substring(0, values.Length - 1);