# 各种基本算法实现小结（六）—— 查找算法

（均已测试通过）

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1、简单查找

#include <stdio.h> #include <stdlib.h> #include <time.h> #define MAX 101 void input(int num[]) { int i; srand((unsigned)time(NULL)); for(i=1; i<MAX; i++) num[i]=rand()%100; } void output(int num[]) { int i; for(i=1; i<MAX; i++) { printf("%5d", num[i]); if(0==i%10) printf("/n"); } } int find(int num[], int x) { int i; for(i=1; i<MAX; i++) if(x == num[i]) return i; return 0; } void main() { int x, pos, num[MAX]; input(num); printf("num...: /n"); output(num); printf("Enter find num: "); scanf("%d", &x); pos=find(num, x); if(pos) printf("OK! %d is found in pos: %d/n", x, pos); else printf("Sorry! %d is not found... in num/n", x); }

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2、 折半查找

#include <stdio.h> #include <stdlib.h> #include <time.h> #define MAX 101 void input(int num[]) { int i; srand((unsigned)time(NULL)); for(i=1; i<MAX; i++) num[i]=rand()%100; } void output(int num[]) { int i; for(i=1; i<MAX; i++) { printf("%5d", num[i]); if(0==i%10) printf("/n"); } } void sort(int num[], int low, int high) /* quick sort */ { int l, h; if(low<high) { l=low; h=high; num[0]=num[l]; /* save pivot */ while(l<h) { while(l<h && num[h]>=num[0]) h--; num[l]=num[h]; while(l<h && num[l]<=num[0]) l++; num[h]=num[l]; } num[l]=num[0]; /* insert pivot */ sort(num, low, l-1); sort(num, l+1, high); } } int find(int num[], int x, int low, int high) { int mid; while(low<=high) { mid=(low+high)/2; /* find is OK */ if(x==num[mid]) return mid; else if(x<num[mid]) high=mid-1; else low=mid+1; } return 0; } void main() { int x, pos, num[MAX]; input(num); printf("sort before... /n"); output(num); sort(num, 1, MAX-1); printf("sort after... /n"); output(num); printf("Enter find num: "); scanf("%d", &x); pos=find(num, x, 1, MAX-1); if(pos) printf("OK! %d is found in pos: %d/n", x, pos); else printf("Sorry! %d is not found... in num/n", x); }

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