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.
1 // Forward declaration of the read4 API.
2 int read4(char *buf);
3
4 class Solution {
5 public:
6 /**
7 * @param buf Destination buffer
8 * @param n Maximum number of characters to read
9 * @return The number of characters read
10 */
11 int read(char *buf, int n) {
12 char tmp[4];
13 int idx = 0, cnt4;
14 while (idx < n) {
15 cnt4 = read4(tmp);
16 for (int i = 0; i < cnt4 && idx < n; ++i) {
17 buf[idx++] = tmp[i];
18 }
19 if (cnt4 < 4) break;
20 }
21 return idx;
22 }
23 };
Read N Characters Given Read4 II - Call multiple times
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.
1 // Forward declaration of the read4 API.
2 int read4(char *buf);
3
4 class Solution {
5 private:
6 char tmp[4];
7 int tmp_idx = 0, tmp_len = 0;
8 public:
9 /**
10 * @param buf Destination buffer
11 * @param n Maximum number of characters to read
12 * @return The number of characters read
13 */
14 int read(char *buf, int n) {
15 int idx = 0;
16 bool flag;
17 while (idx < n) {
18 flag = true;
19 if (tmp_idx == tmp_len) {
20 tmp_idx = 0;
21 tmp_len = read4(tmp);
22 if (tmp_len != 4) flag = false;
23 }
24 for (; tmp_idx < tmp_len && idx < n; ++tmp_idx) {
25 buf[idx++] = tmp[tmp_idx];
26 }
27 if (!flag) break;
28 }
29 return idx;
30 }
31 };