Quick Sort, Sort basics

Fast sorting is the best way to sort the average performance at the moment, and is preferred as an array sort.

The basic idea: to divide an array into the left and right parts with Q as the bounds, the left part is less than Q, the lower part is greater than q; Next, divide and conquer the two parts according to this rule, until it cannot be divided, the array is sorted.

Key: How to divide the left and right parts? Q Which value should I take? (with my stupidity, the approach to the introduction of the algorithm did not understand, so forced himself to think of a solution)

Analysis: Since this array is not sorted (order random), it is better to let the first value of the array is q, smaller than Q on the left, larger than Q to the right, but there is a skill, if the first and then the Q, if compared to the second, if smaller than q to the entire array backwards to insert this small value, If larger than Q, you need to move the array forward.

So instead of setting a variable to the value of the temp p, the first position is empty, first, looking forward to a small value than Q to fill in the first position, then this position will be empty (this position should be used to put a higher value than Q), Then the previous backward looking for a larger value than Q fill in this position (the space time out of the position should be used to put a smaller than Q value), so loop until the previous backward and from the back forward coincident, this position is the position of P (left than Q small, the right is larger than Q)

intDevide (int*a,intLowintHigh ) {    inttemp =A[low];  while(low<High ) {         while(temp<a[high]&&high>Low ) { High--; }//A[low] = A[high];//low++;        if(high>Low ) {A[low]=A[high]; Low++; }         while(temp>a[low]&&high>Low ) { Low++; }//A[high] = A[low];//high--;         if(high>Low ) {A[high]=A[low]; High--; }} A[low]=temp; returnLow ;}

Divide and Conquer:

void quick_sort (int *a,int Low,int. High ) {    if(low< High ) {        int q = devide (a,low,high);        Quick_sort (a,low,q-1);        Quick_sort (a,q+1, high);    }}

Test code:

#include <iostream>using namespacestd;intDevide (int*a,intLowintHigh ) {    inttemp =A[low];  while(low<High ) {         while(temp<a[high]&&high>Low ) { High--; }//A[low] = A[high];//low++;        if(high>Low ) {A[low]=A[high]; Low++; }         while(temp>a[low]&&high>Low ) { Low++; }//A[high] = A[low];//high--;         if(high>Low ) {A[high]=A[low]; High--; }} A[low]=temp; returnLow ;}voidQuick_sort (int*a,intLowintHigh ) {    if(low<High ) {        intQ =devide (A,low,high); Quick_sort (A,low,q-1); Quick_sort (A,q+1, high); }}intMain () {inta[ the];  for(intI=0;i<Ten; i++) {cin>>A[i]; } quick_sort (A,0,9);  for(intI=0;i<Ten; i++) {cout<<a[i]<<" "; }    return 0;}

Quick Sort, Sort basics