What type of algorithm does java's indexOf implement

What type of algorithm does java's indexOf implement

By : Hank Smith
Date : November 20 2020, 01:01 AM
I think the issue was by ths following , ode uses the brute force algorithm to find the substring in a given string. That is, the approach runs in O(mn), where m and n are the length of the source and target strings.
more info here and here
code :

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D2: std.algorithm.indexOf doesn't work anymore

D2: std.algorithm.indexOf doesn't work anymore

By : Tonny
Date : March 29 2020, 07:55 AM
will help you Long story but I'll try to keep it short:
std.algorithm.indexOf expects an input range, which is a structural type that must define front, popFront() and empty. For arrays, these methods are defined in std.array and work via uniform function call syntax, which allows fun(someArray) to work the same as someArray.fun().
code :
void main() {
    immutable string[] s1 = ["a", "b", "c"];
    immutable(string)[] s2 = ["d", "e", "f"];

    s2 = s2[1..$];  // This is what std.array.popFront does under the hood.
    assert(s2 == ["e", "f"]);  // Passes.
    s2[1] = "g";     // Error:  Can't modify immutable data.

    s1 = s1[1..$];  // Error:  Can't modify immutable data.
    s1[1] = "g";    // Error:  Can't modify immutable data.
How to implement the algorithm for HashCash in Go (type conversion issues)?

How to implement the algorithm for HashCash in Go (type conversion issues)?

By : Josh
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I would suggest the following code (the function partialAllZeroes should run much faster):
code :
package main

import "crypto/sha1"

func partialAllZeroes(zeroCount uint8, b []byte) bool {
    i := 0
    for zeroCount >= 8 {
        if b[i] != 0 {
            return false
        zeroCount -= 8

    var mask byte
    switch zeroCount {
    case 0: mask = 0x00
    case 1: mask = 0x01
    case 2: mask = 0x03
    case 3: mask = 0x07
    case 4: mask = 0x0f
    case 5: mask = 0x1f
    case 6: mask = 0x3f
    case 7: mask = 0x7f

    return (b[i] & mask) == 0

func main() {
    hasher := sha1.New()
    baseCollisionString := "BASE COLLISION STRING"
    nonce := "12345"
    hasher.Write([]byte(baseCollisionString + nonce))
    testCollision := hasher.Sum()
    partialAllZeroes(100, testCollision)
What Abstract Data Type (ADT) is used to implement steinhaus-johnson-trotter (permutations) algorithm in Python?

What Abstract Data Type (ADT) is used to implement steinhaus-johnson-trotter (permutations) algorithm in Python?

By : Đorđe Božić
Date : March 29 2020, 07:55 AM
may help you . You don't need to insert new elements into the sequence, you only need to swap two elements each time. This is fast on an array. The standard Python list is implemented as an array, see https://wiki.python.org/moin/TimeComplexity, so I think it's the best data structure for this purpose.
indexOf() : is there a better way to implement this?

indexOf() : is there a better way to implement this?

By : Franc
Date : March 29 2020, 07:55 AM
To fix this issue the question is very vague. however what i understood from the code is that you need to check for string match between two strings.
Since you know its two strings, i'd just pass them as two parameters. additionally i'd change the while into a for statement and add a break/continue to avoid using variable get and set.
code :
mutation bestCase 14.84499999999997
mutation worstCase 7.694999999999993
bestCase: 5.595000000000027
worstCase: 7.199999999999989
// your function (to check performance difference)
function mutation(arr) {

  var stringOne = arr[0].toLowerCase();
  var stringTwo = arr[1].toLowerCase().split("");
  var i = 0;
  var truthyFalsy = true;

  while (i < arr[1].length && truthyFalsy) {

    truthyFalsy = stringOne.indexOf(stringTwo[i]) > -1;

  return truthyFalsy;

function hasMatch(base, check) {
  var strOne = base.toLowerCase();
  var strTwo = check.toLowerCase().split("");

  var truthyFalsy = false;

  // define both variables (i and l) before the loop condition in order to avoid getting the length property of the string multiple times.
  for (var i = 0, l = strTwo.length; i < l; i++) {
    var hasChar = strOne.indexOf(strTwo[i]) > -1;
    if (hasChar) {
      //if has Char, set true and break;
      truthyFalsy = true;
  return truthyFalsy;

var baseCase = "hello";
var bestCaseStr = "hey";
var worstCaseStr = "yap";

//bestCase find match in first iteration
var bestCase = hasMatch("hello", bestCaseStr);

//worstCase loop over all of them.
var worstCase = hasMatch("hello", worstCaseStr);

// on your function
console.log('mutation bestCase', checkPerf(mutation, [baseCase, bestCaseStr]));

console.log('mutation worstCase', checkPerf(mutation, [baseCase, worstCaseStr]));

// simple performance check
console.log('bestCase:', checkPerf(hasMatch, baseCase, bestCaseStr));

console.log('worstCase:', checkPerf(hasMatch, baseCase, worstCaseStr));

function checkPerf(fn) {
  var t1 = performance.now();
  for (var i = 0; i < 10000; i++) {
    fn(arguments[1], arguments[2]);
  var t2 = performance.now();
  return t2 - t1;
How does android.support break Javas type safety?

How does android.support break Javas type safety?

By : Melvin
Date : November 10 2020, 04:01 AM
I hope this helps . The SeekBarPreference object that you end up with in an android.preference.PreferenceActivity is indeed an android.preference.SeekBarPreference. The issue here is that that class is hidden in the SDK (source), so Android Studio will not suggest it for auto-completion, nor will it import it automatically. Since you're using the support libraries in your project, and the support version of SeekBarPreference is publicly available, that will be the class Android Studio tries to use there, thus the conflict.
Unfortunately, PreferenceActivity does not check from where the preference XML is coming, so it will happily create an instance of that platform class whenever it sees a tag. This is arguably a bug, but I'm not sure they'd consider it so, as that class is nowhere mentioned in the documentation.
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