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 may be called multiple times.
和157题一样,区别在于可以对一个文件多次使用read
那么区别就是在于如果之前调用过一次read,可能由于调用了read4的原因,会出现多读了几个字母(小于4个),那么设定一个变量即可。存储当前多读取的字母长度和字母。
1、需要注意的点:多次调用的时候,moreChars里的字母可能没有用完。
/* The read4 API is defined in the parent class Reader4. int read4(char[] buf); */ public class Solution extends Reader4 { /** * @param buf Destination buffer * @param n Maximum number of characters to read * @return The number of characters read */ private int len = 0; private char[] moreChars = new char[3]; public int read(char[] buf, int n) { if (n < 1){ return 0; } int result = 0; if (len != 0){ int count = Math.min(n, len); for (int i = 0; i < count; i++){ buf[i] = moreChars[i]; result++; } for (int i = 0; i < (len - count); i++){ moreChars[i] = moreChars[count + i]; } len -= count; } char[] chars = new char[4]; int times = (n - result) / 4; for (int i = 0; i < times; i++){ int count = read4(chars); for (int j = 0; j < count; j++){ buf[result + j] = chars[j]; } result += count; if (count < 4){ return result; } } if (n == result){ return result; } int count = read4(chars); for (int i = 0; i < Math.min(n - result, count); i++){ buf[result + i] = chars[i]; } if (n - result < count){ len = count - n + result; for (int i = 0; i < len; i++){ moreChars[i] = chars[n - result + i]; } } result += Math.min(n - result, count); return result; } }