49 lines
1.6 KiB
C++
49 lines
1.6 KiB
C++
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// Source : https://oj.leetcode.com/problems/read-n-characters-given-read4/
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// Author : Hao Chen
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// Date : 2014-11-20
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/**********************************************************************************
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*
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* The API: int read4(char *buf) reads 4 characters at a time from a file.
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*
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* The return value is the actual number of characters read.
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* For example, it returns 3 if there is only 3 characters left in the file.
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*
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* By using the read4 API, implement the function int read(char *buf, int n)
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* that reads n characters from the file.
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*
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* Note:
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* The read function will only be called once for each test case.
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*
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**********************************************************************************/
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// Forward declaration of the read4 API.
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int read4(char *buf);
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class Solution {
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public:
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/**
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* @param buf Destination buffer
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* @param n Maximum number of characters to read
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* @return The number of characters read
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*/
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int read(char *buf, int n) {
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char _buf[4]; // the buffer for read4()
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int _n = 0; // the return for read4()
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int len = 0; // total buffer read from read4()
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int size = 0; // how many bytes need be copied from `_buf` to `buf`
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while((_n = read4(_buf)) > 0){
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//check the space of `buf` whether enough or not
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size = len + _n > n ? n-len : _n;
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strncpy(buf+len, _buf, size);
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len += size;
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//buffer is full
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if (len>=n){
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break;
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}
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}
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return len;
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}
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};
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