一道使用了翻手算法解答的算法题

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　　一个未排序整数数组，有正负数，重新排列使负数排在正数前面，并且要求不改变原来的相对顺序比如： input: 1,7,-5,9,-12,15 ans: -5,-12,1,7,9,15 要求时间复杂度O(N),空间O(1) 。

#include <stdio.h>#include <stdlib.h>#include <time.h>#define N 10000#define M 20#define DEBUGvoid reverse(int *left, int *right){while (left < right) {int tmp = *left;*left++ = *right;*right-- = tmp;}}void swap_arr(int *lbegin, int *lend, int *rbegin, int *rend){reverse(lbegin, lend);reverse(rbegin, rend);reverse(lbegin, rend);}/**************** Just for Test ******************/int random1(){int isPos, val;static unsigned seed = 1;srand(seed + (unsigned)time(NULL));seed++;isPos = rand() % 10;val = rand() % 1000;return isPos ? val : -val;}int is_true(int arr[]){int i;for (i = 0; i < N; ++i)if (arr[i] >= 0)break;for ( ; i < N; ++i)if (arr[i] < 0)break;return i == N ? 1 : 0;}/**************** Just for Test ******************/int main(){int arr[N];int *lbegin, *lend, *rbegin, *rend;int i;#ifdef DEBUGFILE *fp;fp = fopen("arr_swap.out", "w");if (fp == NULL) {printf("cannot open this file\n");exit (0);}#endiffor (i = 0; i < N; ++i)arr[i] = random1();for (i = 0; i < N; ++i)if (arr[i] >= 0)break;lbegin = &arr[i];for ( ; i < N; ++i) {if (arr[i] < 0) {lend = &arr[i-1];rbegin = &arr[i];for (; i < N; ++i) if (arr[i] >= 0)break;rend = &arr[--i];swap_arr(lbegin, lend, rbegin, rend);lbegin += ((rend - rbegin) / sizeof(int *) + 1);}}#ifdef DEBUGfor (i = 0; i < N; ++i) {if ( (i%M) == (M-1))fputc('\n', fp);fprintf(fp, "%d ", arr[i]);}fclose(fp);#endifif (is_true(arr) == 1)printf("true\n");return 0;}