Update word_break.cpp

Author: caba5

Diff for: cpp/neetcode_150/13_1-d_dynamic_programming/word_break.cpp

@@ -7,7 +7,7 @@
     Time: O(n^3)
     Space: O(n)
 */
-
+/*
 class Solution {
 public:
     bool wordBreak(string s, vector<string>& wordDict) {
@@ -35,3 +35,37 @@ class Solution {
         return dp[n];
     }
 };
+*/
+
+/*
+    Given a string & dictionary, return true if:
+    Can segment string into 1 or more dictionary words
+
+    Bottom-up DP: for each position in the string, loop over
+    the words in the dictionary. If the word matches the substring
+    starting at the current position, assign to the DP array in the 
+    same position the same value of the DP array at position + matched_word
+    length.
+
+    Time: O(n^2 * m)
+    Space: O(n)
+*/
+class Solution {
+public:
+    bool wordBreak(string s, vector<string>& wordDict) {
+        int strSize = s.size();
+        vector<bool> dp(strSize + 1);
+        dp[strSize] = true;
+
+        for (int i = strSize - 1; i >= 0; --i){
+            for (string& w : wordDict){
+                if (i + w.size() <= strSize && s.substr(i, w.size()) == w)
+                    dp[i] = dp[i + w.size()];
+                if (dp[i])
+                    break;
+            }
+        }
+
+        return dp[0];
+    }
+};