重点：

  1. midmid 取 l+rl+r 还是 l+r+1l+r+1。

  2. " == " 的话应该算那种情况。

代码：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
#include<cstdio>
#include<algorithm>
using namespace std;
#define re register
const int MAXn = 1e4;

template <class T>
inline void read(T &a) {
    register char c;while (c = getchar(), (c < '0' || c > '9') && c != '-');register bool f = c == '-';register T x = f ? 0 : c - '0';while (c = getchar(), c >= '0' && c <= '9') {x = (x << 3) + (x << 1) + (c ^ 48);}a = f ? -x : x;
}

int n, x, arr[MAXn + 10];
int a() {					//大于等于中最小的(lower_bound)
    int l = 1, r = n;
    while (l < r) {
        int mid = (l + r) >> 1;
        if (arr[mid] >= x) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    return l;
}
int b() {					//大于中最小的(upper_bound)
    int l = 1, r = n;
    while (l < r) {
        int mid = (l + r) >> 1;
        if (arr[mid] > x) {
            r = mid;
        } else {
            l = mid + 1;
        }
    }
    return l;
}
int c() {					//小于中最大的
    int l = 1, r = n;
    while (l < r) {
        int mid = (l + r + 1) >> 1;
        if (arr[mid] >= x) {
            r = mid - 1;
        } else {
            l = mid;
        }
    }
    return l;
}
int d() {					//小于等于中最大的
    int l = 1, r = n;
    while (l < r) {
        int mid = (l + r + 1) >> 1;
        if (arr[mid] > x) {
            r = mid - 1;
        } else {
            l = mid;
        }
    }  
    return l;
}

int main() {
    read(n), read(x);
    for (re int i = 1; i <= n; ++i) {
        read(arr[i]);
    }
    printf("%d %d %d %d\n", a(), b(), c(), d());
    // printf("%d %d\n", int(lower_bound(arr + 1, arr + 1 + n, x) - arr), int(upper_bound(arr + 1, arr + 1 + n, x) - arr));
}

结果：