【算法】 分治

二分查找

#include<stdio.h>
void sort(int *a , int n) {
    
    int temp = 0 ;
    for(int i = 0 ; i < n ; i++) 
    {
        for(int j = 0 ; j < n ; j++ )
        if(a[j] > a[j+1])
        {
            temp = a[j];
            a[j] = a[j+1];
            a[j+1] = temp;
        }
        if(temp == 0)
        break;
    }
    
} 

int BinarySearch(int *a , int high , int data) {
    int low = 0;
    int mind = (low + high)/2;
    while(low <= high)
    {    
        if(a[mind] == data)
        return mind;
        if(a[mind] > data)
        high = mind - 1 ;
        if(a[mind] < data )
        low = mind + 1;
        mind = (low + high)/2 ;    
    }
    return -1 ;
}

int BinarySearchDG(int *a , int high , int low , int data) {
    mind = (low + high) / 2 ;
    if(a[mind] == data)
    return -1;
    if(a[mind] > data)
    BinarySearchDG(a , high , mind + 1 , data);
    if(a[mind] < data)
    BinarySearchDG(a , mind - 1 , low , data);
}

void printOut(int *a , int n ) {
    int i = 0;
    while(i < n)
    printf("%d
", a[i++]);

}

int main() {
    int a[] = {18,26,3,4,5,60,56,37};
    sort(a , 8);
    printOut(a , 8 );
    int m = BinarySearch(a , 8 , 18);
    printf("%d" , m );
}

 归并排序

#include<stdio.h>

void PrintSort(int *a , int high) {
    int i = 0 ;
    while(i <= high)
    {
        printf("%d---
" , a[i++]);
    }
}

void Merge(int *a , int low , int mind , int high) {
    int *b = new int[high - low + 1];
    int h = 0 , i , j , k = 0;
    for( i = low , j = mind + 1 ; i <= mind && j <= high ; )
    {
        if(a[i] >= a[j])
        b[h++] = a[i++];
        else
        b[h++] = a[j++];
    }
    while( j <= high ) {
        b[h++] = a[j++];
    }
    
    while( i <= mind ) {
        b[h++] = a[i++];
    }
    h = low ;
    while(h <= high) 
    a[h++] = b[k++];
    
}

void MergeSort(int *a , int low , int high) {
    int mind ;
    if(high > low) {
        mind = (low + high) / 2;
        MergeSort(a ,  low , mind);
        MergeSort(a ,  mind+1 , high);
        Merge(a , low , mind , high);
    }
}


int main () {
    int a[] = {1,2,1,2,3,5,6};
    MergeSort(a , 0 , 6);
    PrintSort(a , 6);
} 

 快速排序

#include<stdio.h>

void swap( int &a1 , int &a2 ) {
    int data;
    data = a1;
     a1 = a2 ;
     a2 = data;
}

int Partition(int *a , int low , int high) { // 划分方法，每次划分后使 
    int pivot = a[low] , i , j ;
    for( i = low , j = high ; i < j ; ) {    //pivot = a[low] 处于该数组的最终位置 
        while(a[j] >= pivot && j > i )       //若尾部元素大于指针元素，则继续向前移动 j-- 
            j--;
        if( j > i )
            swap(a[i++] , a[j]);
        while(a[i] < pivot && j > i )       //若首部元素小于指针元素，则向后移动 i++ 
            i++;
        if( j > i )
            swap(a[j--] , a[i]);
    }
    
    return j ;
}

void QuickSort(int *a , int low , int high) { //递归，不断将问题进行划分 ，化成更小的问题 
    int index;
    if(low < high) {                          //判断是否到达栈低 
        index = Partition( a , low , high);
        QuickSort( a , low , index - 1 );
        QuickSort( a , index + 1 , high);
    }
}

void PrintArray(int *a , int n) {
    for(int i = 0 ; i < n ; )
    printf("  %d  " , a[i++]); 
    printf("
");
}

int main() {
    int a[10] = {1,55,6,5,4154,5,46546,787846,775};
    PrintArray(a , 10);
    QuickSort(a , 0 , 9);
    PrintArray(a , 10);     
}