191 lines
3.7 KiB
C
191 lines
3.7 KiB
C
/*************************************************************************
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> File Name: bsearch.c
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> Author: jinshaohui
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> Mail: jinshaohui789@163.com
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> Time: 18-10-21
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> Desc:
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************************************************************************/
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#include<stdio.h>
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#include<stdlib.h>
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#include<assert.h>
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/*二分查找算法的变形问题
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*1、查找第一个等于给定数值的元素
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*2、查找最后一个等于给定数值的元素
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*3、查找第一个大于等于给定数值的元素
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*4、查找第一个小于等于给定数值的元素
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* */
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/*1、查找第一个等于给定数值的元素*/
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int mybsearch_1(int a[],int size,int value)
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{
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int mid = 0;
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int left = 0;
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int right = size - 1;
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while(left <= right)
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{
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/*防止size数量太大是，（left + right）数据翻转，导致问题*/
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mid = left + ((right - left)>>1);
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if (a[mid] < value)
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{
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left = mid + 1;
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}
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else if (a[mid] > value)
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{
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right = mid - 1;
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}
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else
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{
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if ((mid == 0) || (a[mid - 1] != value))
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{
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return mid;
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}
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else
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{
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right = mid - 1;
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}
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}
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}
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return -1;
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}
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/*2、查找最后一个等于给定数值的元素*/
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int mybsearch_2(int a[],int size,int value)
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{
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int mid = 0;
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int left = 0;
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int right = size - 1;
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while(left <= right)
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{
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/*防止size数量太大是，（left + right）数据翻转，导致问题*/
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mid = left + ((right - left)>>1);
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if (a[mid] < value)
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{
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left = mid + 1;
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}
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else if (a[mid] > value)
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{
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right = mid - 1;
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}
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else
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{
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if ((mid == (size - 1)) || (a[mid + 1] != value))
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{
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return mid;
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}
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else
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{
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left = mid + 1;
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}
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}
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}
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return -1;
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}
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/*3、查找第一个大于等于给定数值的元素*/
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int mybsearch_3(int a[],int size,int value)
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{
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int mid = 0;
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int left = 0;
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int right = size - 1;
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while(left <= right)
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{
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/*防止size数量太大是，（left + right）数据翻转，导致问题*/
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mid = left + ((right - left)>>1);
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if (a[mid] < value)
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{
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left = mid + 1;
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}
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else
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{
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/*a[mid] >= value 当mid==0 或者a[mid-1] > value 说明是第一个大于等于value*/
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if ((mid == 0) || (a[mid - 1] < value))
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{
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return mid;
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}
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else
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{
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right = mid - 1;
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}
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}
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}
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return -1;
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}
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/*4、查找第一个小于等于给定数值的元素*/
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int mybsearch_4(int a[],int size,int value)
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{
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int mid = 0;
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int left = 0;
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int right = size - 1;
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while(left <= right)
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{
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/*防止size数量太大是，（left + right）数据翻转，导致问题*/
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mid = left + ((right - left)>>1);
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if (a[mid] > value)
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{
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right = mid - 1;
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}
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else
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{
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/*a[mid] <= value 时，当前mid == size -1 数组中最大的数值；
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* 或者a[mid + 1] 大于vlaue，就是mid就第一个小于等于value*/
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if ((mid == (size - 1)) || (a[mid + 1] > value))
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{
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return mid;
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}
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else
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{
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left = mid + 1;
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}
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}
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}
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return -1;
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}
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int main()
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{
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int a[10] = {5,6,6,9,10,11,11,22,33,33};
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int data = 0;
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int i = 0;
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int res =0;
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printf("\r\n");
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for(i = 0; i < 10 ; i++)
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{
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printf("%d ",a[i]);
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}
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printf("\r\n");
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printf("\r\n输入一个整数");
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scanf("%d",&data);
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res = mybsearch_1(a,10,data);
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printf("第一个等于data[%d]，下标是%d",data,res);
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printf("\r\n输入一个整数");
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scanf("%d",&data);
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res = mybsearch_2(a,10,data);
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printf("最后一个等于data[%d]，下标是%d",data,res);
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printf("\r\n输入一个整数");
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scanf("%d",&data);
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res = mybsearch_2(a,10,data);
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printf("第一个大于等于data[%d]，下标是%d",data,res);
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printf("\r\n输入一个整数");
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scanf("%d",&data);
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res = mybsearch_2(a,10,data);
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printf("第一个小等于data[%d]，下标是%d",data,res);
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return;
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}
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