Adding _1081.java

README.md

@@ -1031,7 +1031,7 @@ _If you like this project, please leave me a star._ ★
 | 319  |[Bulb Switcher](https://leetcode.com/problems/bulb-switcher/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_319.java)                                                                  |                                                                               |Medium| Brainteaser
 | 318  |[Maximum Product of Word Lengths](https://leetcode.com/problems/maximum-product-of-word-lengths/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_318.java)                                                                  |                                                                               |Medium| 
 | 317  |[Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_317.java)                                                                  |                                                                               |Hard| 
-| 316  |[Remove Duplicate Letters](https://leetcode.com/problems/remove-duplicate-letters/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_316.java)                                                                  |                                                                               |Hard| Stack, Recursion, Greedy
+| 316  |[Remove Duplicate Letters](https://leetcode.com/problems/remove-duplicate-letters/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_316.java)                                                                  |                                                                               |Medium| Stack, Recursion, Greedy
 | 315  |[Count of Smaller Numbers After Self](https://leetcode.com/problems/count-of-smaller-numbers-after-self/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_315.java)                                                                  |                                                                               |Hard| Tree
 | 314  |[Binary Tree Vertical Order Traversal](https://leetcode.com/problems/binary-tree-vertical-order-traversal/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_314.java)                                                                  |                                                                               |Medium| HashMap, BFS
 | 313  |[Super Ugly Number](https://leetcode.com/problems/super-ugly-number/)| [Solution](../master/src/main/java/com/fishercoder/solutions/_313.java)                                                                  |                                                                               |Medium| 

_1081.java

@@ -0,0 +1,44 @@
+package com.fishercoder.solutions;
+
+import java.util.*;
+
+// same as 316. Remove Duplicate Letters
+// from https://github.com/fishercoder1534/Leetcode/blob/master/src/main/java/com/fishercoder/solutions/_316.java
+
+public class _1002 {
+    public class Solution1 {
+        public String smallestSubsequence(String s) {
+            int[] res = new int[26]; //will contain number of occurences of character (i+'a')
+            boolean[] visited =
+                    new boolean[26]; //will contain if character (i+'a') is present in current result Stack
+                    char[] ch = s.toCharArray();
+            for (char c : ch) {  //count number of occurences of character
+                res[c - 'a']++;
+            }
+            Deque<Character> st = new ArrayDeque<>(); // answer stack
+            int index;
+            for (char c : ch) {
+                index = c - 'a';
+                res[index]--;   //decrement number of characters remaining in the string to be analysed
+                if (visited[index]) {
+                    //if character is already present in stack, dont bother
+                    continue;
+                }
+                //if current character is smaller than last character in stack which occurs later in the string again
+                //it can be removed and  added later e.g stack = bc remaining string abc then a can pop b and then c
+                while (!st.isEmpty() && c < st.peek() && res[st.peek() - 'a'] != 0) {
+                    visited[st.pop() - 'a'] = false;
+                }
+                st.push(c); //add current character and mark it as visited
+                visited[index] = true;
+            }
+
+            StringBuilder sb = new StringBuilder();
+            //pop character from stack and build answer string from back
+            while (!st.isEmpty()) {
+                sb.insert(0, st.pop());
+            }
+            return sb.toString();
+        }
+    }
+}

src/main/java/com/fishercoder/solutions/1961. Check If String Is a Prefix of Array.java

@@ -0,0 +1,21 @@
+package com.fishercoder.solutions;
+
+public class _1961{
+    public class Solution1 {
+        public boolean isPrefixString(String s, String[] words) {
+
+            String t="";
+            int i=0;
+
+            while(t.length()<s.length() && i<words.length){
+                t+=words[i++];
+
+                if(t.equals(s))
+                    return true;
+            }
+
+            return false;
+
+        }
+    }
+}

src/main/java/com/fishercoder/solutions/_881.java

@@ -57,4 +57,28 @@ public int numRescueBoats(int[] people, int limit) {
             return boats;
         }
     }
+
+    public static class Solution2 {
+        public int numRescueBoats(int[] people, int limit) {
+            Arrays.sort(people);
+            int end = people.length - 1;
+            int start = 0;
+            int boatcount = 0;
+            while (end >= start) {
+                if (people[end] == limit) {
+                    end--;
+                    boatcount++;
+                } else if (people[end] + people[start] <= limit) {
+                    start++;
+                    end--;
+                    boatcount++;
+                } else {
+                    end--;
+                    boatcount++;
+                }
+            }
+            return boatcount;
+        }
+    }
+
 }