如果输入数据总量 ≥ 10^5，则应该考虑使用快读。
尤其是：总整数个数 ≥ 100000，或输入文件大小 ≥ 几 MB
且语言是 Java，因为 Java 的 Scanner 会非常慢，本质上是“正则解析器”，时间复杂度远高于预期。
static class FastScanner {private final InputStream in = System.in;private final byte[] buffer = new byte[1 << 16];private int ptr = 0, len = 0;private int read() throws IOException {if (ptr >= len) {len = in.read(buffer);ptr = 0;if (len == -1) return -1;}return buffer[ptr++];}int nextInt() throws IOException {int c;while ((c = read()) <= ' ') {if (c == -1) return -1;}int sign = 1;if (c == '-') {sign = -1;c = read();}int val = c - '0';while ((c = read()) > ' ') {val = val * 10 + (c - '0');}return val * sign;}
}