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2014-11-20 17:59:45 +08:00
// Source : https://oj.leetcode.com/problems/read-n-characters-given-read4/
// Author : Hao Chen
// Date : 2014-11-20
/**********************************************************************************
*
* 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 read4 API, implement the function int read(char *buf, int n)
* that reads n characters from the file.
*
* Note:
* The read function will only be called once for each test case.
*
**********************************************************************************/
// 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) {
char _buf[4]; // the buffer for read4()
int _n = 0; // the return for read4()
int len = 0; // total buffer read from read4()
int size = 0; // how many bytes need be copied from `_buf` to `buf`
while((_n = read4(_buf)) > 0){
//check the space of `buf` whether enough or not
size = len + _n > n ? n-len : _n;
strncpy(buf+len, _buf, size);
len += size;
//buffer is full
if (len>=n){
break;
}
}
return len;
}
};