hihoCoder#1128 二分·二分查找

原题地址

一开始没搞懂题目是想干什么，于是写了一个扫一遍的代码，A了，如下：

代码：

 1 #include <iostream>
 2
 3 using namespace std;
 4
 5 int main() {
 6   int N, K, a;
 7   bool found = false;
 8   int lt = 0;
 9
10   scanf("%d%d", &N, &K);
11   for (int i = 0; i < N; i++) {
12     scanf("%d", &a);
13     if (a == K)
14       found = true;
15     if (a < K)
16       lt++;
17   }
18   printf("%d\n", (found ? lt + 1 : -1));
19
20   return 0;
21 }

做到后面一题的时候才明白题目是什么意思，代码如下：

 1 #include <iostream>
 2
 3 using namespace std;
 4
 5 #define SIZE 100000
 6
 7 int N, K;
 8 int a[SIZE];
 9
10 int ltc(int left, int right) {
11   if (left >= right)
12     return 0;
13
14   int l = left;
15   int r = right;
16   int p = a[left];
17
18   while (l < r) {
19     while (l < r && a[r] > p)
20       r--;
21     a[l] = a[r];
22     while (l < r && a[l] < p)
23       l++;
24     a[r] = a[l];
25   }
26   a[l] = p;
27
28   if (a[l] == K)
29     return l - left;
30   else if (a[l] < K)
31     return l - left + 1 + ltc(l + 1, right);
32   else
33     return ltc(left, l - 1);
34 }
35
36 int main() {
37   bool found = false;
38
39   scanf("%d%d", &N, &K);
40   for (int i = 0; i < N; i++) {
41     scanf("%d", &(a[i]));
42     found |= (a[i] == K);
43   }
44
45   printf("%d\n", (found ? ltc(0, N - 1) + 1: -1));
46
47   return 0;
48 }