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Author: ayoubzulfiqar

ReadNCharactersGivenRead4/read_n_characters_given_read4.dart

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+/*
+
+
+Given a file and assume that you can only read the file using a given method read4, implement a method to read n characters.
+Method read4:
+The API read4 reads four consecutive characters from file, then writes those characters into the buffer array buf4.
+The return value is the number of actual characters read.
+Note that read4() has its own file pointer, much like FILE *fp in C.
+Definition of read4:
+    Parameter:  char[] buf4
+    Returns:    int
+
+buf4[] is a destination, not a source. The results from read4 will be copied to buf4[].
+Below is a high-level example of how read4 works:
+File file("abcde"); // File is "abcde", initially file pointer (fp) points to 'a'
+char[] buf4 = new char[4]; // Create buffer with enough space to store characters
+read4(buf4); // read4 returns 4. Now buf4 = "abcd", fp points to 'e'
+read4(buf4); // read4 returns 1. Now buf4 = "e", fp points to end of file
+read4(buf4); // read4 returns 0. Now buf4 = "", fp points to end of file
+Method read:
+By using the read4 method, implement the method read that reads n characters from file and store it in the buffer array buf. Consider that you cannot manipulate file directly.
+The return value is the number of actual characters read.
+Definition of read:
+    Parameters:	char[] buf, int n
+    Returns:	int
+
+buf[] is a destination, not a source. You will need to write the results to buf[].
+Note:
+Consider that you cannot manipulate the file directly. The file is only accessible for read4 but not for read.
+The read function will only be called once for each test case.
+You may assume the destination buffer array, buf, is guaranteed to have enough space for storing ncharacters.
+Example 1:
+Input: file = "abc", n = 4
+Output: 3
+Explanation: After calling your read method, buf should contain "abc". We read a total of 3 characters from the file, so return 3.
+Note that "abc" is the file's content, not buf. buf is the destination buffer that you will have to write the results to.
+Example 2:
+Input: file = "abcde", n = 5
+Output: 5
+Explanation: After calling your read method, buf should contain "abcde". We read a total of 5 characters from the file, so return 5.
+Example 3:
+Input: file = "abcdABCD1234", n = 12
+Output: 12
+Explanation: After calling your read method, buf should contain "abcdABCD1234". We read a total of 12 characters from the file, so return 12.
+Example 4:
+Input: file = "leetcode", n = 5
+Output: 5
+Explanation: After calling your read method, buf should contain "leetc". We read a total of 5 characters from the file, so return 5.
+Constraints:
+1 <= file.length <= 500
+file consist of English letters and digits.
+1 <= n <= 1000
+
+*/
+
+/*
+
+
+APPROACH 1
+
+
+As we know, we have to implement the ‘READ’ method using the ‘READ4’ method.
+
+So first, we call the ‘READ4’ method and pass a ‘TEMP_BUFFER’ array/list of 4 sizes.
+And this method returns the number of characters reads from the ‘FILE’ and all these characters are
+stored in this ‘TEMP_BUFFER’ array/list. When we read the ‘N’ characters from the ‘FILE’ we return the number of actual
+characters that are read from ‘FILE’.
+
+
+
+
+As we know, the ‘READ’ method is called any number of times. So we have to store the remaining
+characters of the ‘TEMP_BUFFER’ array/list also. So that's why we declare this ‘TEMP_BUFFER’
+array/list as a global variable.
+
+
+
+Here is the algorithm:
+
+
+
+We declare an array/list ‘TEMP_BUFFER’ of size 4 in which we store the current 4 characters of the ‘FILE’.
+We declare two variables ‘TEMP_POINTER’ and ‘TEMP_COUNT’ where ‘TEMP_POINTER’ points to the location of the
+current character in ‘TEMP_BUFFER’ and  ‘TEMP_COUNT’ stores how many characters are present in ‘TEMP_BUFFER’.
+We declare a variable ‘COUNTER’ which represents the number of characters read from the ‘FILE’.
+We run a loop while ‘COUNTER’ less than ‘N’:
+If ‘TEMP_POINTER’ == 0:
+‘TEMP_COUNT’ = ‘READ4[‘TEMP_BUFFER’].
+If ‘TEMP_COUNT’ == 0:
+Break.
+We run a loop while ‘COUNTER’ less than ‘N’ and ‘TEMP_POINTER’ less than ‘TEMP_COUNT’:
+BUFFER[POINTER] =  ‘TEMP_BUFFER[‘TEMP_POINTER’]’
+POINTER.
+‘TEMP_POINTER’.
+If ‘TEMP_POINTER’ equal to ‘TEMP_COUNT’:
+‘TEMP_POINTER’ = 0.
+Return ‘COUNTER’.
+
+
+*/
+
+abstract class Reader4 {
+  int read4(List<int> buf4);
+}
+
+class Solution extends Reader4 {
+  int read(List<int> buf, int n) {
+    List<int> buf4 = [4];
+    int i4 = 0; // buf4's index
+    int n4 = 0; // buf4's size
+    int i = 0; // buf's index
+    while (i < n) {
+      if (i4 == n4) {
+        // all characters in buf4 are consumed
+        i4 = 0; // reset buf4's index
+        n4 = read4(buf4); // read 4 (or less) chars from file to buf4
+        if (n4 == 0) // reach the EOF
+          return i;
+      }
+      buf[i++] = buf4[i4++];
+    }
+
+    return i;
+  }
+
+  @override
+  int read4(List<int> buf4) {
+    throw UnimplementedError();
+  }
+}
+
+class Solution2 extends Reader4 {
+  int read(List<int> buf, int n) {
+    int copyCharIndex = 0;
+    int charRead = 4;
+    List<int> buf4 = List.filled(4, 0);
+    while (copyCharIndex < n && charRead == 4) {
+      charRead = read4(buf4);
+      for (var i = 0; i < charRead; i++) {
+        if (copyCharIndex == n) {
+          return n;
+        }
+        buf[copyCharIndex++] = buf4[i];
+      }
+    }
+    return copyCharIndex;
+  }
+
+  @override
+  int read4(List<int> buf4) {
+    throw UnimplementedError();
+  }
+}

ReadNCharactersGivenRead4/read_n_characters_given_read4.go

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+package main

ReadNCharactersGivenRead4/read_n_characters_given_read4.md

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+# 🔥 DART || Read N Characters Given Read4 Solution || with Explanation
+
+## Reader4 Class
+
+### Or
+
+```dart
+// if you don't wanna override
+class Reader4 {
+  int read4(List<int> buf4){
+      return 0;
+  }
+}
+```
+
+```dart
+abstract class Reader4 {
+  int read4(List<int> buf4);
+}
+```
+
+```dart
+class Solution extends Reader4 {
+  int read(List<int> buf, int n) {
+    int copyCharIndex = 0;
+    int charRead = 4;
+    List<int> buf4 = List.filled(4, 0);
+    while (copyCharIndex < n && charRead == 4) {
+        // charRead = Reader4().read4(buf4)
+      charRead = read4(buf4);
+      for (var i = 0; i < charRead; i++) {
+        if (copyCharIndex == n) {
+          return n;
+        }
+        buf[copyCharIndex++] = buf4[i];
+      }
+    }
+    return copyCharIndex;
+  }
+
+
+// this override is because of abstract class
+  @override
+  int read4(List<int> buf4) {
+    throw UnimplementedError();
+  }
+}
+```
+
+## Solution - 2
+
+```dart
+class Solution extends Reader4 {
+  int read(List<int> buf, int n) {
+    List<int> buf4 = [4];
+    int i4 = 0; // buf4's index
+    int n4 = 0; // buf4's size
+    int i = 0; // buf's index
+    while (i < n) {
+      if (i4 == n4) {
+        // all characters in buf4 are consumed
+        i4 = 0; // reset buf4's index
+        // charRead = Reader4().read4(buf4)
+        n4 = read4(buf4); // read 4 (or less) chars from file to buf4
+        if (n4 == 0) // reach the EOF
+          return i;
+      }
+      buf[i++] = buf4[i4++];
+    }
+
+    return i;
+  }
+
+  @override
+  int read4(List<int> buf4) {
+    throw UnimplementedError();
+  }
+}
+```