adding lecture 21

leetcode/p1451_rearrange_words_in_a_sentence.cpp

@@ -0,0 +1,46 @@
+// solution to leetcode 1451
+
+class Solution {
+    public:
+        static bool cmp(std::pair<string,int> p1, std::pair<string,int> p2){
+        //bool cmp(string p1, string p2){
+            int len1 = p1.first.length();
+            int len2 = p2.first.length();
+            if(len1==len2){
+                // keep the original order
+                return (p1.second<p2.second);
+            }else{
+                return (len1<len2);
+            }
+        }
+
+        string arrangeWords(string text) {
+            string ans;
+            // store all words and its index.
+            vector<std::pair<string, int>> v1;
+            string word;
+            int index;
+            char c;
+            c=tolower(text[0]);
+            text[0]=c;
+            // store the words and its index into v1.
+            stringstream ss(text);
+            while(ss >> word){  // if there are n words, O(n)
+                v1.push_back({word, index});
+                index++;
+            }
+            std:sort(v1.begin(), v1.end(), cmp);
+            int size;
+            size = v1.size();
+            for(int i=0;i<size-1;i++){  // if there are n words, O(n)
+                ans += v1[i].first;    // step 1. call operator+()
+                                            // step 2. call operator=(),
+                                            // step 3. call operator+=();
+                ans += ' ';
+            }
+            ans = ans + v1[size-1].first;
+            c=toupper(ans[0]);
+            ans[0]=c;
+            return ans;
+        }
+};