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第一:
顺序表查找
从线性表中的第一个 ( 或最后一个 ) 数据元素开 始 , 逐个进行数据元素关键字和给定值的比较 ,若某个数据元素的关键字和给定值相等则查找成 功 ; 如果直到最后一个 ( 或第一个 ) 数据元素 , 其关键字和给定值都不等时 , 则查找失败.
顺序表查找
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 20
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
void print_array(int a[], int begin, int end)
{
int i = 0;
for(i=begin; i<=end; i++)
{
printf("%d, ", a[i]);
}
printf("\n");
}
int another_search(int a[], int len, int key)
{
int ret = len;
a[0] = key;
while( a[ret] != key )
{
ret--;
}
return ret;
}
int main(int argc, char *argv[])
{
int a[SIZE + 1] = {0};
int i = 0;
int key = 0;
int index = 0;
srand((unsigned int)time(NULL));
for(i=1; i<=SIZE; i++)
{
a[i] = rand() % 100;
}
key = rand() % 100;
printf("Another Search Demo\n");
printf("Key: %d\n", key);
printf("Array: \n");
print_array(a, 1, SIZE);
index = another_search(a, SIZE, key);
if( index > 0 )
{
printf("Success: a[%d] = %d\n", index, a[index]);
}
else
{
printf("Failed!\n");
}
return 0;
}
第二:
二分查找
? 基本思想
? 首先将查找表进行排序
? 取中间数据元素进行比较
查 当给定值与中间数据元素的关键字相等时 , 查找成功
在 当给定值小于中间元素时 , 在中间元素左区间进行二分查找
在 当给定值大于中间元素时 , 在中间元素右区间进行二分查找
? 查 当任意区间均无记录时 , 查找失败
二分查找
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 20
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
void println(int array[], int len)
{
int i = 0;
for(i=0; i<len; i++)
{
printf("%d ", array[i]);
}
printf("\n");
}
void swap(int array[], int i, int j)
{
int temp = array[i];
array[i] = array[j];
array[j] = temp;
}
void SelectionSort(int array[], int len) // O(n*n)
{
int i = 0;
int j = 0;
int k = -1;
for(i=0; i<len; i++)
{
k = i;
for(j=i; j<len; j++)
{
if( array[j] < array[k] )
{
k = j;
}
}
swap(array, i, k);
}
}
int binary_search(int a[], int low, int high, int key) // O(logn)
{
int ret = -1;
if( low <= high )
{
int mid = (low + high) / 2;
if( a[mid] == key )
{
ret = mid;
}
else if( key < a[mid] )
{
ret = binary_search(a, low, mid-1, key);
}
else if( key > a[mid] )
{
ret = binary_search(a, mid+1, high, key);
}
}
return ret;
}
int binary_search_ex(int a[], int low, int high, int key) // O(logn)
{
int ret = -1;
while( low <= high )
{
int mid = (low + high) / 2;
if( a[mid] == key )
{
ret = mid;
break;
}
else if( key < a[mid] )
{
high = mid - 1;
}
else if( key > a[mid] )
{
low = mid + 1;
}
}
return ret;
}
int interpolation_search(int a[], int low, int high, int key)
{
int ret = -1;
while( (low <= high) && (a[low] <= key) && (key <= a[high]) )
{
float fx = 1.0f * (key - a[low]) / (a[high] - a[low]);
int mid = low + fx * (high - low);
if( a[mid] == key )
{
ret = mid;
break;
}
else if( key < a[mid] )
{
high = mid - 1;
}
else if( key > a[mid] )
{
low = mid + 1;
}
}
return ret;
}
int main(int argc, char *argv[])
{
int a[SIZE] = {0};
int i = 0;
int key = 0;
int index = 0;
srand((unsigned int)time(NULL));
for(i=1; i<=SIZE; i++)
{
a[i] = rand() % 100;
}
key = 50;
printf("Binary Search Demo\n");
printf("Key: %d\n", key);
printf("Array: \n");
SelectionSort(a, SIZE);
println(a, SIZE);
index = interpolation_search(a, 0, SIZE-1, key);
if( index > 0 )
{
printf("Success: a[%d] = %d\n", index, a[index]);
}
else
{
printf("Failed!\n");
}
return 0;
}
第三:
插值查找
小结
顺序查找比较土,但却是其他查找算法的基础
? 二分查找基于有序的线性表 , 时间复杂度提高到O(logn)
? 二分查找可以根据需要进一步演变为插值查找