157 Read N Characters Given Read4
The API:
int read4(char *buf)reads 4 characters at a time from a file.The return value is the actual number of characters read. For example, it returns 3 if there is only 3 characters left in the file.
By using the
read4API, implement the functionint read(char *buf, int n)that readsncharacters from the file.Note:
The
readfunction will only be called once for each test case.The Idea: Buffer in 4 characters at a time until we either run out of characters to read, or the amount we read exceeds n. Modify the nth buffer to be the empty character for any offset issues.
Complexity: O(n/4) time and O(1) space
// Forward declaration of the read4 API.
int read4(char *buf);
class Solution {
public:
/**
* @param buf Destination buffer
* @param n Maximum number of characters to read
* @return The number of characters read
*/
int read(char *buf, int n) {
int total_read = 0;
int cur_read = 0;
do {
cur_read = read4(buf + total_read);
total_read += cur_read;
} while (cur_read == 4 && total_read < n);
buf[n] = '\0';
return total_read;
}
};
Last modified 3yr ago