Added 2 solutions & modified 1 solution

Author: varunu28

Easy/Running Sum of 1d Array.java

@@ -0,0 +1,11 @@
+class Solution {
+  public int[] runningSum(int[] nums) {
+    int[] ans = new int[nums.length];
+    int sum = 0;
+    for (int i = 0; i < nums.length; i++) {
+      sum += nums[i];
+      ans[i] = sum;
+    }
+    return ans;
+  }
+}

Medium/Least Number of Unique Integers after K Removals.java

@@ -0,0 +1,28 @@
+class Solution {
+  public int findLeastNumOfUniqueInts(int[] arr, int k) {
+    Map<Integer, Integer> map = new HashMap<>();
+    List<Integer> list = new ArrayList<>();
+    for (int num : arr) {
+      if (!map.containsKey(num)) {
+        list.add(num);
+      }
+      map.put(num, map.getOrDefault(num, 0) + 1);
+    }
+    Collections.sort(list, new Comparator<Integer>(){
+      public int compare(Integer o1, Integer o2) {
+        return map.get(o1) - map.get(o2);
+      }
+    });
+    for (Integer num : list) {
+      int count = map.get(num);
+      k -= count;
+      if (k >= 0) {
+        map.remove(num);
+      }
+      else {
+       break; 
+      }
+    }
+    return map.size();
+  }
+}

Medium/Replace Words.java

@@ -1,63 +1,56 @@
 class Solution {
-    
-    public String replaceWords(List<String> dict, String sentence) {
-
-        Map<String, Integer> map = new HashMap<>();
-
-        for (String s: dict) {
-            map.put(s, s.length());
-        }
-
-        Map<String, Integer> sortedMap = sortByValue(map);
-
-        String[] arr = sentence.split("\\s");
-        String[] ans = new String[arr.length];
-        int j = 0;
-
-        for (String s : arr) {
-            boolean gotIt = false;
-            for (Map.Entry<String,Integer> entry : sortedMap.entrySet()) {
-                if (s.startsWith(entry.getKey())) {
-                    ans[j] = entry.getKey();
-                    gotIt = true;
-                    break;
-                }
-            }
-
-            if (!gotIt) {
-                ans[j] = s;
-            }
-
-            j++;
-        }
-
-        StringBuilder ansString = new StringBuilder("");
-
-        for (String s : ans) {
-            ansString.append(s + " ");
-        }
-
-        return ansString.toString().trim();
+  public String replaceWords(List<String> dict, String sentence) {
+    Node root = new Node('-');
+    for (String word : dict) {
+      addWord(word, 0, root);
     }
-
-    private Map<String, Integer> sortByValue(Map<String, Integer> unsortMap) {
-
-        List<Map.Entry<String, Integer>> list =
-                new LinkedList<Map.Entry<String, Integer>>(unsortMap.entrySet());
-
-        Collections.sort(list, new Comparator<Map.Entry<String, Integer>>() {
-            public int compare(Map.Entry<String, Integer> o1,
-                               Map.Entry<String, Integer> o2) {
-                return (o1.getValue()).compareTo(o2.getValue());
-            }
-        });
-
-        Map<String, Integer> sortedMap = new LinkedHashMap<String, Integer>();
-        for (Map.Entry<String, Integer> entry : list) {
-            sortedMap.put(entry.getKey(), entry.getValue());
-        }
-
-        return sortedMap;
+    String[] words = sentence.split("\\s+");
+    for (int i = 0; i < words.length; i++) {
+      String prefix = getPrefix(words[i], root);
+      if (prefix != null) {
+        words[i] = prefix;
+      }
+    }
+    return String.join(" ", words);
+  }
+  
+  private String getPrefix(String word, Node root) {
+    for (int i = 0; i < word.length(); i++) {
+      if (!root.children.containsKey(word.charAt(i))) {
+        return null;
+      }
+      root = root.children.get(word.charAt(i));
+      if (root.word != null) {
+        return root.word;
+      }
     }
+    return null;
+  }
+  
+  private void addWord(String word, int idx, Node root) {
+    if (idx == word.length()) {
+      return;
+    }
+    if (!root.children.containsKey(word.charAt(idx))) {
+      root.children.put(word.charAt(idx), new Node(word.charAt(idx)));
+    }
+    root = root.children.get(word.charAt(idx));
+    if (idx == word.length() - 1) {
+      root.word = word;
+    }
+    addWord(word, idx + 1, root);
+  }
+}
+
 
+class Node {
+  char c;
+  Map<Character, Node> children;
+  String word;
+  
+  public Node(char c) {
+    this.c = c;
+    children = new HashMap<>();
+    word = null;
+  }
 }