day 20

Author: sachuverma

Leetcode Daily Challenge/December-2020/20. Decoded String at Index.cpp

@@ -0,0 +1,68 @@
+/*
+Decoded String at Index
+=======================
+
+An encoded string S is given.  To find and write the decoded string to a tape, the encoded string is read one character at a time and the following steps are taken:
+
+If the character read is a letter, that letter is written onto the tape.
+If the character read is a digit (say d), the entire current tape is repeatedly written d-1 more times in total.
+Now for some encoded string S, and an index K, find and return the K-th letter (1 indexed) in the decoded string.
+
+Example 1:
+Input: S = "leet2code3", K = 10
+Output: "o"
+Explanation: 
+The decoded string is "leetleetcodeleetleetcodeleetleetcode".
+The 10th letter in the string is "o".
+
+Example 2:
+Input: S = "ha22", K = 5
+Output: "h"
+Explanation: 
+The decoded string is "hahahaha".  The 5th letter is "h".
+
+Example 3:
+Input: S = "a2345678999999999999999", K = 1
+Output: "a"
+Explanation: 
+The decoded string is "a" repeated 8301530446056247680 times.  The 1st letter is "a".
+
+Constraints:
+2 <= S.length <= 100
+S will only contain lowercase letters and digits 2 through 9.
+S starts with a letter.
+1 <= K <= 10^9
+It's guaranteed that K is less than or equal to the length of the decoded string.
+The decoded string is guaranteed to have less than 2^63 letters.
+*/
+
+class Solution
+{
+public:
+  string decodeAtIndex(string S, int K)
+  {
+    long size = 0;
+    int N = S.size();
+
+    for (int i = 0; i < N; ++i)
+    {
+      if (isdigit(S[i]))
+        size *= S[i] - '0';
+      else
+        size++;
+    }
+
+    for (int i = N - 1; i >= 0; --i)
+    {
+      K %= size;
+      if (K == 0 && isalpha(S[i]))
+        return (string) "" + S[i];
+
+      if (isdigit(S[i]))
+        size /= S[i] - '0';
+      else
+        size--;
+    }
+    return "";
+  }
+};

Leetcode Daily Challenge/December-2020/README.md

@@ -21,5 +21,5 @@
 | 17. | [4Sum II](https://leetcode.com/explore/challenge/card/december-leetcoding-challenge/571/week-3-december-15th-december-21st/3569/)              |          [cpp](./17.%204Sum%20II.cpp)           |
 | 18. | [Increasing Triplet Subsequence](https://leetcode.com/explore/challenge/card/december-leetcoding-challenge/571/week-3-december-15th-december-21st/3570/)              |          [cpp](./18.%20Increasing%20Triplet%20Subsequence.cpp)           |
 | 19. | [Cherry Pickup II](https://leetcode.com/explore/challenge/card/december-leetcoding-challenge/571/week-3-december-15th-december-21st/3571/)              |          [cpp](./19.%20Cherry%20Pickup%20II.cpp)   |    
-| 20. | []() |[cpp](./20.%20.cpp)   |    
+| 20. | [Decoded String at Index](https://leetcode.com/explore/challenge/card/december-leetcoding-challenge/571/week-3-december-15th-december-21st/3572/) |[cpp](./20.%20Decoded%20String%20at%20Index.cpp)   |    
 | 21. | [Smallest Range II](https://leetcode.com/explore/challenge/card/december-leetcoding-challenge/571/week-3-december-15th-december-21st/3573/) |[cpp](./21.%20Smallest%20Range%20II.cpp)   |