Leetcode30

dsa-solutions/lc-solutions/0000-0099/0030-Substring-with-Concatenation-of-All-Words.md

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+---
+id: substring-with-concatenation-of-all-words
+title: Substring with Concatenation of All Words (LeetCode)
+sidebar_label: 0030-SubstringWithConcatenationOfAllWords
+description: Find the starting indices of all substrings in the given string that are the concatenation of each word in a given list exactly once and without any intervening characters.
+---
+
+## Problem Description
+
+| Problem Statement | Solution Link | LeetCode Profile |
+| :---------------- | :------------ | :--------------- |
+| [Substring with Concatenation of All Words](https://leetcode.com/problems/subtitle-with-concatenation-of-all-words/) | [Substring with Concatenation of All Words Solution on LeetCode](https://leetcode.com/problems/subtitle-with-concatenation-of-all-words/solutions/) | [vaishu_1904](https://leetcode.com/u/vaishu_1904/) |
+
+## Problem Description
+
+You are given a string `s` and an array of strings `words`. All the strings of `words` are of the same length.
+
+Return all starting indices of substring(s) in `s` that are the concatenation of each word in `words` exactly once, in any order, and without any intervening characters.
+
+You can return the answer in any order.
+
+**Example:**
+
+#### Example 1
+
+- **Input:** `s = "barfoothefoobarman"`, `words = ["foo","bar"]`
+- **Output:** `[0, 9]`
+- **Explanation:** Substrings starting at indices 0 and 9 are "barfoo" and "foobar" respectively. The output order does not matter, returning `[9, 0]` is fine too.
+
+#### Example 2
+
+- **Input:** `s = "wordgoodgoodgoodbestword"`, `words = ["word","good","best","word"]`
+- **Output:** `[]`
+
+#### Example 3
+
+- **Input:** `s = "barfoofoobarthefoobarman"`, `words = ["bar","foo","the"]`
+- **Output:** `[6,9,12]`
+
+### Constraints
+
+- `1 <= s.length <= 10^4`
+- `s` consists of lower-case English letters.
+- `1 <= words.length <= 5000`
+- `1 <= words[i].length <= 30`
+- `words[i]` consists of lower-case English letters.
+
+### Approach
+
+To solve this problem, we need to find all starting indices of substrings in `s` that are the concatenation of all words in `words`. Here’s a step-by-step approach:
+
+1. **Initialization**:
+   - Calculate the length of each word (`word_len`), the number of words (`num_words`), and the total length of the concatenated substring (`substring_len`).
+
+2. **Sliding Window**:
+   - Use a sliding window to check every possible starting index in `s`.
+   - For each starting index, check if the substring from that index can be formed by concatenating all words exactly once.
+
+3. **Hash Map**:
+   - Use a hash map to store the frequency of each word in `words`.
+   - For each window, use another hash map to count the frequency of words found in the current window.
+
+4. **Validation**:
+   - Validate if the frequency of words in the current window matches the frequency of words in the given list.
+
+### Solution Code
+
+#### Python
+
+```python
+class Solution:
+    def findSubstring(self, s, words):
+        if not s or not words:
+            return []
+
+        word_len = len(words[0])
+        num_words = len(words)
+        substring_len = word_len * num_words
+        word_count = collections.Counter(words)
+
+        result = []
+
+        for i in range(word_len):
+            left = i
+            right = i
+            current_count = collections.Counter()
+            while right + word_len <= len(s):
+                word = s[right:right + word_len]
+                right += word_len
+                if word in word_count:
+                    current_count[word] += 1
+                    while current_count[word] > word_count[word]:
+                        current_count[s[left:left + word_len]] -= 1
+                        left += word_len
+                    if right - left == substring_len:
+                        result.append(left)
+                else:
+                    current_count.clear()
+                    left = right
+        return result
+```
+#### Java
+```java
+import java.util.*;
+
+class Solution {
+    public List<Integer> findSubstring(String s, String[] words) {
+        List<Integer> result = new ArrayList<>();
+        if (s == null || s.length() == 0 || words == null || words.length == 0)
+            return result;
+
+        int wordLen = words[0].length();
+        int numWords = words.length;
+        int substringLen = wordLen * numWords;
+
+        Map<String, Integer> wordCount = new HashMap<>();
+        for (String word : words) {
+            wordCount.put(word, wordCount.getOrDefault(word, 0) + 1);
+        }
+
+        for (int i = 0; i < wordLen; i++) {
+            int left = i, right = i;
+            Map<String, Integer> currentCount = new HashMap<>();
+            while (right + wordLen <= s.length()) {
+                String word = s.substring(right, right + wordLen);
+                right += wordLen;
+                if (wordCount.containsKey(word)) {
+                    currentCount.put(word, currentCount.getOrDefault(word, 0) + 1);
+                    while (currentCount.get(word) > wordCount.get(word)) {
+                        String leftWord = s.substring(left, left + wordLen);
+                        currentCount.put(leftWord, currentCount.get(leftWord) - 1);
+                        left += wordLen;
+                    }
+                    if (right - left == substringLen) {
+                        result.add(left);
+                    }
+                } else {
+                    currentCount.clear();
+                    left = right;
+                }
+            }
+        }
+
+        return result;
+    }
+}
+```
+
+#### c++
+
+```c++
+#include <vector>
+#include <string>
+#include <unordered_map>
+using namespace std;
+
+class Solution {
+public:
+    vector<int> findSubstring(string s, vector<string>& words) {
+        vector<int> result;
+        if (s.empty() || words.empty())
+            return result;
+
+        int wordLen = words[0].size();
+        int numWords = words.size();
+        int substringLen = wordLen * numWords;
+
+        unordered_map<string, int> wordCount;
+        for (const string& word : words) {
+            wordCount[word]++;
+        }
+
+        for (int i = 0; i < wordLen; ++i) {
+            int left = i, right = i;
+            unordered_map<string, int> currentCount;
+            while (right + wordLen <= s.size()) {
+                string word = s.substr(right, wordLen);
+                right += wordLen;
+                if (wordCount.find(word) != wordCount.end()) {
+                    currentCount[word]++;
+                    while (currentCount[word] > wordCount[word]) {
+                        string leftWord = s.substr(left, wordLen);
+                        currentCount[leftWord]--;
+                        left += wordLen;
+                    }
+                    if (right - left == substringLen) {
+                        result.push_back(left);
+                    }
+                } else {
+                    currentCount.clear();
+                    left = right;
+                }
+            }
+        }
+
+        return result;
+    }
+};
+```
+
+### Conclusion
+The solution efficiently finds all starting indices of substrings in s that are the concatenation of all words in words using a sliding window approach and hash maps. This approach ensures that the integer division truncates toward zero as required, and handles edge cases and constraints effectively.