递归1--二分查找
递归1--二分查找
一、心得
递归的时候注意返回值，返回的时候是返回到上一层
二、代码及结果
1 /* 2 二分查找： 3 可写递推和递归 4 其实这两个都只要把递推式子写出来就好 5 6 查找的数大于mid，left=mid+1 7 小于mid，right=mid-1 8 边界条件，等于mid，输出即可 9 */ 10 /* 11 心得：注意返回值，返回的时候是返回到上一层 12 */ 13 #include <iostream> 14 using namespace std; 15 //二分查找递归，设置标签 16 bool binarySearch1(int a[],int left,int right,int num){//初始left=0，right=length-1 17 bool flag=false; 18 int mid=(left+right)/2; 19 //cout<<mid<<endl; 20 //cout<<num<<" "<<a[mid]<<endl; 21 if(left<=right){ 22 if(num==a[mid]) { 23 flag=true; 24 } 25 else if(num>a[mid]){ 26 //cout<<"right:"<<a[mid+1]<<" "<<a[right]<<endl; 27 flag=binarySearch1(a,mid+1,right,num); 28 29 } 30 else if(num<a[mid]){ 31 //cout<<"left:"<<a[left]<<" "<<a[mid-1]<<endl; 32 flag=binarySearch1(a,left,mid-1,num); 33 } 34 } 35 return flag; 36 } 37 38 //二分查找非递归，不设置标签 39 /* 40 不设置返回值的时候，有栈可以存值 41 */ 42 bool binarySearch2(int a[],int left,int right,int num){//初始left=0，right=length-1 43 44 int mid=(left+right)/2; 45 //cout<<mid<<endl; 46 //cout<<num<<" "<<a[mid]<<endl; 47 if(left<=right){ 48 if(num==a[mid]) { 49 return true; 50 } 51 else if(num>a[mid]){ 52 //cout<<"right:"<<a[mid+1]<<" "<<a[right]<<endl; 53 binarySearch2(a,mid+1,right,num); 54 55 } 56 else if(num<a[mid]){ 57 //cout<<"left:"<<a[left]<<" "<<a[mid-1]<<endl; 58 binarySearch2(a,left,mid-1,num); 59 } 60 } 61 else{ 62 return false; 63 } 64 } 65 66 67 //二分查找递推 68 bool binarySearch3(int a[],int left,int right,int num){//初始left=0，right=length-1 69 while(left<=right){ 70 int mid=(left+right)/2; 71 if(num==a[mid]) return true; 72 else if(num>a[mid]) left=mid+1; 73 else if(num<a[mid]) right=mid-1; 74 } 75 return false; 76 } 77 78 int main(){ 79 int a[11]={1,2,4,7,8,9,11,15,17,19,20}; 80 //bool b=binarySearch1(a,0,10,20); 81 //bool b=binarySearch2(a,0,10,7); 82 bool b=binarySearch3(a,0,10,20); 83 cout<<b<<endl; 84 return 0; 85 }
