快速排序递归和非递归算法

int partition(int q[],int low,int high) {int i=low; int j=high+1; int p=i; while(1){ while(q[++i]<q[p]); while(q[--j]>q[p]); if(i>=j) break; swap(q[i],q[j]);} swap(q[j],q[p]); return j; } /*递归算法*/ void quicksort(int q[],int low,int high) { if(low<high) {int p=partition2(q,low,high); quicksort(q,low,p-1); quicksort(q,p+1,high);} }

 

以下是非递归算法

A non-recursive version of quick sort using stack: There are 2 stacks, namely one which stores the start of a subarray and the other which stores the end of the subarray. STEP 1: while the subarray contains more than one element ,i.e. from<to Do { SUBSTEP 1. pivot=Partion(subarray); SUBSTEP 2. keep track of the right half of the current subarray i.e. push (pivot+1) into stackFrom, push (to) into stackTo SUBSTEP 3. go on to deal with the left half of the current subarray i.e. to=pivot-1 } STEP 2: if(neither of the stacks is empty) Get a new subarray to deal with from the stacks. i.e. start=pop(stackFrom); to=pop(stackTo); STEP 3: both stacks are empty, and array has been sorted. The program ends. */*/ void UnrecQuicksort(int q[],int low,int high) {stack<int> s1; stack<int>s2; s1.push(low); s2.push(high); int tl,th,p; while(!s1.empty() && !s2.empty()) {tl=s1.top();th=s2.top(); s1.pop();s2.pop(); if(tl>=th) continue; p=partition(q,tl,th); s1.push(tl);s1.push(p+1); s2.push(p-1);s2.push(th); } }