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solves #30: Substring with Concatenation of All Words in java
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-18
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‎README.md

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| 27 | [Remove Element](https://leetcode.com/problems/remove-element/) | [![Java](assets/java.png)](src/RemoveElement.java) [![Python](assets/python.png)](python/remove_element.py) | |
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| 28 | [Needle in Haystack](https://leetcode.com/problems/implement-strstr) | [![Java](assets/java.png)](src/NeedleInHaystack.java) [![Python](assets/python.png)](python/needle_in_haystack.py) | |
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| 29 | [Divide Two Integers](https://leetcode.com/problems/divide-two-integers) | [![Java](assets/java.png)](src/DivideTwoIntegers.java) | |
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| 30 | [Substring with Concatenation of All Words](https://leetcode.com/problems/substring-with-concatenation-of-all-words) | [![Java](assets/java.png)](src/SubstringWithConcatenationOfAllWords.java) | |
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| 31 | [Next Permutation](https://leetcode.com/problems/next-permutation) | [![Java](assets/java.png)](src/NextPermutation.java) | |
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| 33 | [Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array) | [![Java](assets/java.png)](src/SearchInRotatedSortedArray.java) | |
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| 34 | [Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array) | [![Java](assets/java.png)](src/FindFirstAndLastPositionOfElementInSortedArray.java) | |

‎src/HelloWorld.java

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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Collections;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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public class HelloWorld {
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public int strStr(String haystack, String needle) {
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if (needle.length() > haystack.length()) {
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return -1;
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public int lengthOfLongestSubstring(String s) {
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if (s.isEmpty()) {
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return 0;
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}
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for (int i = 0 ; i < haystack.length() ; i++) {
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if (needle.charAt(0) == haystack.charAt(i) && containsAt(haystack, needle, i)) {
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return i;
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int maxLength = 1;
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final Set<Character> slidingWindow = new HashSet<>() {{
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add(s.charAt(0));
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}};
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for (int left = 0, right = 1, currentLength = 1 ; right < s.length() ; ) {
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if (slidingWindow.contains(s.charAt(right))) {
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slidingWindow.remove(s.charAt(left));
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left++;
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currentLength--;
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} else {
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slidingWindow.add(s.charAt(right));
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currentLength++;
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maxLength = Math.max(maxLength, currentLength);
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right++;
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}
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}
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return -1;
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}
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private static boolean containsAt(String haystack, String needle, int i) {
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if (needle.length() > haystack.length() - i) {
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return false;
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}
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for (int index = i + 1 ; index < haystack.length() && index - i < needle.length() ; index++) {
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if (needle.charAt(index - i) != haystack.charAt(index)) {
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return false;
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}
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}
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return true;
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return maxLength;
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}
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}

‎src/SubstringWithConcatenationOfAllWords.java

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// https://leetcode.com/problems/substring-with-concatenation-of-all-words
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// T: O(|words| + |s| * |words[i]|)
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// S: O(|words| + |words[i]|)
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import java.util.ArrayList;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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class SubstringWithConcatenationOfAllWords {
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private final Map<String, Integer> wordCount = new HashMap<>();
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private int n;
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private int wordLength;
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private int substringSize;
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private int k;
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private void slidingWindow(int left, String s, List<Integer> answer) {
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HashMap<String, Integer> wordsFound = new HashMap<>();
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int wordsUsed = 0;
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boolean excessWord = false;
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// Do the same iteration pattern as the previous approach - iterate
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// word_length at a time, and at each iteration we focus on one word
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for (int right = left; right <= n - wordLength; right += wordLength) {
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String sub = s.substring(right, right + wordLength);
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if (!wordCount.containsKey(sub)) {
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// Mismatched word - reset the window
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wordsFound.clear();
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wordsUsed = 0;
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excessWord = false;
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left = right + wordLength;
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} else {
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// If we reached max window size or have an excess word
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while (right - left == substringSize || excessWord) {
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String leftmostWord = s.substring(left, left + wordLength);
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left += wordLength;
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wordsFound.put(
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leftmostWord,
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wordsFound.get(leftmostWord) - 1
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);
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if (
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wordsFound.get(leftmostWord) >=
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wordCount.get(leftmostWord)
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) {
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// This word was an excess word
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excessWord = false;
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} else {
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// Otherwise we actually needed it
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wordsUsed--;
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}
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}
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// Keep track of how many times this word occurs in the window
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wordsFound.put(sub, wordsFound.getOrDefault(sub, 0) + 1);
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if (wordsFound.get(sub) <= wordCount.get(sub)) {
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wordsUsed++;
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} else {
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// Found too many instances already
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excessWord = true;
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}
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if (wordsUsed == k && !excessWord) {
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// Found a valid substring
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answer.add(left);
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}
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}
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}
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}
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public List<Integer> findSubstring(String s, String[] words) {
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n = s.length();
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k = words.length;
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wordLength = words[0].length();
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substringSize = wordLength * k;
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for (String word : words) {
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wordCount.put(word, wordCount.getOrDefault(word, 0) + 1);
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}
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List<Integer> answer = new ArrayList<>();
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for (int i = 0; i < wordLength; i++) {
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slidingWindow(i, s, answer);
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}
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return answer;
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}
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}

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