编程珠玑 Pearls(1)

[TOC]

使用常量来设置、清除以及测试位值：

提示：MASK 0x1f 2的SHIFT(5)次方，32位,把int型的变量每一位都当作一个标记。

/* Copyright (C) 1999 Lucent Technologies *//* From 'Programming Pearls' by Jon Bentley *//* bitsort.c -- bitmap sort from Column 1 *   Sort distinct integers in the range [0..N-1] */#include <stdio.h>#define BITSPERWORD 32#define SHIFT 5#define MASK 0x1F#define N 10000000int a[1 + N/BITSPERWORD];void set(int i) {        a[i>>SHIFT] |=  (1<<(i & MASK)); }void clr(int i) {        a[i>>SHIFT] &= ~(1<<(i & MASK)); }int  test(int i){ return a[i>>SHIFT] &   (1<<(i & MASK)); }int main(){   int i;    for (i = 0; i < N; i++)        clr(i);/*  Replace above 2 lines with below 3 for word-parallel init    int top = 1 + N/BITSPERWORD;    for (i = 0; i < top; i++)        a[i] = 0; */    while (scanf("%d", &i) != EOF)        set(i);    for (i = 0; i < N; i++)        if (test(i))            printf("%d\n", i);    return 0;}

使用qsort快速排序

提示：
void qsort(voidbase,size_t num,size_t width,int(__cdeclcompare)(const void,const void));
各参数：1. 待排序数组首地址 2. 数组中待排序元素数量 3. 各元素的占用空间大小 4. 指向函数的指针

#include <stdio.h>#include <stdlib.h>int intcomp(int *x, int *y){   return *x - *y;}int a[1000000];int main(){   int i, n=0;    while (scanf("%d", &a[n]) != EOF)        n++;    qsort(a, n, sizeof(int), intcomp);    for (i = 0; i < n; i++)        printf("%d\n", a[i]);    return 0;}

使用标准库版本的排序

#include <iostream>#include <set>using namespace std;int main(){   set<int> S;    int i;    set<int>::iterator j;    while (cin >> i)        S.insert(i);    for (j = S.begin(); j != S.end(); ++j)        cout << *j << "\n";    return 0;}

1.6 习题

1.4 . 如何生成位于0至n-1之间的k个不同的随机顺序的随机整数? 尽量使你的程序简短且高效。

//生k个成0~n-1之间的随机数(k<n) #include<iostream>#include<time.h>#include <stdlib.h>     /* srand, rand */using namespace std; int const N = 10000;int a[N];int main(void){    int i,j,k=10;    for(i = 0 ;i < N; i++)        a[i] = i;    //初始化随机种子，产生随机数     srand((unsigned)time(NULL));    for(i = 0 ; i < k; i ++)    {        int tmp = rand() % (N - i);         cout << "tmp ->" << tmp << endl;        swap(a[tmp],a[N-i]);    }    for(i = N - 1 ; i > N - k;i--)    {        cout<<a[i]<<endl;    }    return 0;} 

1.6 增强，生成区间内的随机数，注意生成的随机数各不相同

/* Copyright (C) 1999 Lucent Technologies *//* From 'Programming Pearls' by Jon Bentley *//* bitsortgen.c -- gen $1 distinct integers from U[0,$2) */#include <stdio.h>#include <stdlib.h>#include <time.h>#define MAXN 2000000int x[MAXN];int randint(int a, int b){   return a + (RAND_MAX * rand() + rand()) % (b + 1 - a);}int main(int argc, char *argv[]){   int i, k, n, t, p;    srand((unsigned) time(NULL));    k = atoi(argv[1]);    n = atoi(argv[2]);    for (i = 0; i < n; i++)        x[i] = i;    for (i = 0; i < k; i++) {        p = randint(i, n-1);        t = x[p]; x[p] = x[i]; x[i] = t;        printf("%d\n", x[i]);    }    return 0;}