插值搜索

       插值搜索核心代码由二分搜索(区间左闭右开)m = l + 1.0/2*(r - 1 - l) = 1.0(l + r - 1)/2 更改为m = l +1.0*(key - a[l])/(a[r - 1] - a[l])*(r - 1 - l).

       利用关键字所在位置的估值(key - a[l])/(a[r - 1] - a[l])代替1/2,对于随机分布为常规分布的关键字,平均时间复杂度lg lg N.即如果N为10亿,平均查找小于5次.

////  main.cpp//  插值搜索////  Created by Lance on 13-3-14.//  Copyright (c) 2013年 Lance. All rights reserved.//#include <iostream>#include <cstdio>using std::cin;using std::cout;using std::endl;typedef int Item;#define key(A)(A)#define less(A, B)(key(A) < key(B))#define exch(A, B){ Item t = A; A = B; B = t; }#define compexch(A, B)if (less(B, A)) exch(A, B)void insertion (Item a[], int l, int r) {//插入排序inti;for (i = r - 1; i > 1; --i)//设置观察哨compexch(a[i - 1], a[i]);for (i = l + 2; i < r; ++i) {intj = i;Itemv = a[i];while (less(v, a[j - 1])) {//确定位置并移位数组a[j] = a[j - 1];--j;} // end of whilea[j] = v;}}Item search (Item a[], Item key, int l, int r) {//插值搜索核心代码intm = l + 1.0*(key - a[l])/(a[r - 1] - a[l])*(r - 1 - l);if (l > r)return -1;if (key == a[m])return m;if (key <  a[m])return search(a, key, l, m);elsereturn search(a, key, m + 1, r);}int main(int argc, char *argv[]) {    const int   N(10);    int         i(0);    Item         *a = new Item[N];        for (i = 0; i < N; ++i)        a[i] = 1000*(1.0*rand()/RAND_MAX);Itemcompare(a[N/2]);        printf("old data:\n");    for (i = 0; i < N; ++i)        printf("%3d ", a[i]);   //便于格式控制    printf("\n");        insertion(a, 0, N);    printf("sorted:\n");    for (i = 0; i < N; ++i)        printf("%3d ", a[i]);    printf("\n");int ans = search(a, compare, 0, N) + 1;cout << endl << endl;cout << "compare is " << compare << endl;cout << "ans is " << ans << endl;    delete a;}