UVA-846 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;    

}