UVA846 Steps 二分查找

不管你是怎么做的，反正我是用二分做的，相当于做了一个预处理。一个最优的序列一定是 1 2 3 .. N .. 3 2 1，或者是 1 2 3 .. N N .. 3 2 1.

代码如下：

#include <cstdlib>
#include <cstdio>
using namespace std;

long long rec[131100], a, b;

void pre()
{
    rec[1] = 1;
    long long LIM = 1LL << 32, base = 1;
    int i;
    for (i = 2; rec[i-1] <= LIM; ++i)    {
        rec[i] = rec[i-1] + base;
        if (!(i & 1)) base++;
    } 
}

int bsearch(int l, int r, long long val)
{
    int mid, ret;
    while (l <= r) {
        mid = (l + r) >> 1;
        if (rec[mid] > val) {
            ret = mid;
            r = mid - 1;
        }
        else if (rec[mid] < val) {
            l = mid + 1;    
        }
        else {
            ret = mid;
            break;    
        }
    }
    return ret;
}

int main()
{
    pre();
    int T;
    scanf("%d", &T);
    while (T--) {
        scanf("%I64d %I64d", &a, &b);
        if (a == b) {
            puts("0");
            continue;
        }
        printf("%d\n", bsearch(1, 131072, b-a));
    }
    return 0;    
}