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In this approach, we use dynamic programming to solve the problem. We define a DP array where dp[i] represents the minimum number of extra characters from index 0 to i of the string s. Initially, we set dp[0] to 0 because there are no extra characters in an empty prefix. For each index i while iterating through the string s, we check every j from 0 to i-1 and see if substring s[j:i] exists in the dictionary. If yes, we update dp[i] to min(dp[i], dp[j]), otherwise, we set dp[i] to dp[i-1] + 1.
Time Complexity: O(N^2*M), where N is the length of the string s and M is the average length of words in the dictionary.
Space Complexity: O(N) because of the DP array.
1#include <stdio.h>
2#include <string.h>
3#include <stdbool.h>
4
5#define MAX_LENGTH 51
6
7bool isInDictionary(char *word, char dictionary[][MAX_LENGTH], int dictionarySize) {
8 for (int i = 0; i < dictionarySize; i++) {
9 if (strcmp(word, dictionary[i]) == 0) {
10 return true;
11 }
12 }
13 return false;
14}
15
16int minExtraChars(char *s, char dictionary[][MAX_LENGTH], int dictionarySize) {
17 int n = strlen(s);
18 int dp[n + 1];
19 for (int i = 0; i <= n; i++) {
20 dp[i] = i;
21 }
22 dp[0] = 0;
23 for (int i = 1; i <= n; i++) {
24 dp[i] = dp[i - 1] + 1;
25 for (int j = 0; j < i; j++) {
26 char sub[i - j + 1];
27 strncpy(sub, s + j, i - j);
28 sub[i - j] = '\0';
29 if (isInDictionary(sub, dictionary, dictionarySize)) {
30 if (dp[j] < dp[i]) {
31 dp[i] = dp[j];
32 }
33 }
34 }
35 }
36 return dp[n];
37}
38
39int main() {
40 char s[] = "leetscode";
41 char dictionary[][MAX_LENGTH] = {"leet", "code", "leetcode"};
42 int dictionarySize = 3;
43 int result = minExtraChars(s, dictionary, dictionarySize);
44 printf("%d\n", result); // Output: 1
45 return 0;
46}This C solution uses a dynamic array to store the minimum number of extra characters needed for each prefix of the string. For each end index i, we check all starting indices to see if a substring is in the dictionary and update the DP accordingly, minimizing extra characters added.
To solve the problem using a Trie and memoization, we first build a Trie from the dictionary. We then use a recursive function with memoization to attempt to decompose the string s into valid segments. For each position in the string, we check possible substrings against the Trie, saving calculated results to avoid redundant computations.
Time Complexity: O(N*M), with N being the string length and M the average dictionary word length due to Trie traversal.
Space Complexity: O(N + T), N is for the memo array and T is for Trie storage.
1using System.Collections.Generic;
class TrieNode {
public Dictionary<char, TrieNode> Children = new Dictionary<char, TrieNode>();
public bool IsEnd;
}
class Trie {
public TrieNode Root = new TrieNode();
public void Insert(string word) {
var node = Root;
foreach (var ch in word) {
if (!node.Children.ContainsKey(ch))
node.Children[ch] = new TrieNode();
node = node.Children[ch];
}
node.IsEnd = true;
}
}
class Solution {
private int MinExtraHelper(string s, int idx, TrieNode root, int[] memo) {
int n = s.Length;
if (idx == n) return 0;
if (memo[idx] != -1) return memo[idx];
int minExtra = n - idx;
TrieNode node = root;
for (int i = idx; i < n; i++) {
if (!node.Children.ContainsKey(s[i])) break;
node = node.Children[s[i]];
if (node.IsEnd)
minExtra = Math.Min(minExtra, MinExtraHelper(s, i + 1, root, memo));
}
minExtra = Math.Min(minExtra, 1 + MinExtraHelper(s, idx + 1, root, memo));
return memo[idx] = minExtra;
}
public int MinExtraChars(string s, List<string> dictionary) {
Trie trie = new Trie();
foreach (var word in dictionary)
trie.Insert(word);
int n = s.Length;
int[] memo = new int[n];
Array.Fill(memo, -1);
return MinExtraHelper(s, 0, trie.Root, memo);
}
static void Main(string[] args) {
var s = "leetscode";
var dictionary = new List<string> { "leet", "code", "leetcode" };
var solution = new Solution();
Console.WriteLine(solution.MinExtraChars(s, dictionary)); // Output: 1
}
}This C# solution constructs a Trie for dictionary look-up and uses a recursive approach with memoization to optimize computations, reducing the number of unmatched characters by leveraging the Trie to find valid words swiftly.