adding word break DP approach

dynamic_programming/word_break.cpp

@@ -0,0 +1,77 @@
+
+/*
+Given a non-empty string s and a dictionary wordDict containing a list of
+non-empty words, determine if s can be segmented into a space-separated sequence
+of one or more dictionary words.
+
+Note:
+
+The same word in the dictionary may be reused multiple times in the
+segmentation. You may assume the dictionary does not contain duplicate words.
+Example 1:
+
+Input: s = "leetcode", wordDict = ["leet", "code"]
+Output: true
+Explanation: Return true because "leetcode" can be segmented as "leet code".
+Example 2:
+
+Input: s = "applepenapple", wordDict = ["apple", "pen"]
+Output: true
+Explanation: Return true because "applepenapple" can be segmented as "apple pen
+apple". Note that you are allowed to reuse a dictionary word. Example 3:
+
+Input: s = "catsandog", wordDict = ["cats", "dog", "sand", "and", "cat"]
+Output: false
+*/
+
+#include <iostream>
+#include <locale>
+#include <queue>
+#include <regex>
+#include <sstream>
+#include <stack>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+using namespace std;
+
+class Solution {
+ public:
+    bool exists(string s, unordered_set<string> strSet) {
+        return strSet.find(s) != strSet.end();
+    }
+
+    bool check(string s, unordered_set<string> strSet, int pos,
+               vector<int>& dp) {
+        if (pos == s.length()) {
+            return true;
+        }
+
+        if (dp[pos] != INT_MAX) {
+            return dp[pos] == 1;
+        }
+
+        string wordTillNow = "";
+        for (int i = pos; i < s.length(); i++) {
+            wordTillNow += string(1, s[i]);
+            if (exists(wordTillNow, strSet) and check(s, strSet, i + 1, dp)) {
+                dp[pos] = 1;
+                return true;
+            }
+        }
+        dp[pos] = 0;
+        return false;
+    }
+
+    bool wordBreak(string s, vector<string>& wordDict) {
+        unordered_set<string> strSet;
+        for (auto s : wordDict) {
+            strSet.insert(s);
+        }
+
+        vector<int> dp(s.length(), INT_MAX);
+        return check(s, strSet, 0, dp);
+    }
+};