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//给定n个整数的集合S和另一个整数x,该算法能确定S中是否存在两个数其和刚好为x#include <stdio.h>
#include <stdbool.h>
#include <malloc.h>int merge(int * objary,unsigned int index_start,unsigned int index_middle,unsigned int index_end)
{int n1 = index_middle - index_start + 1;int n2 = index_end - index_middle;int * leftary = (int *)malloc(n1 * sizeof(int));int * rightary = (int *)malloc(n2 * sizeof(int));int i,j,k = index_start;for(i = 0;i < n1; ++i){leftary[i] = objary[k];k ++;}for(j = 0;j < n2; ++j){rightary[j] = objary[k];k ++;}i = 0;j = 0;for(k = index_start; k <= index_end; ++ k){if(leftary[i] <= rightary[j]){objary[k] = leftary[i];++ i;if(i == n1)break;}else{objary[k] = rightary[j];++ j;if(j == n2)break;}}++ k;if(i == n1){for(; j < n2; ++ j){objary[k] = rightary[j];++ k;}}else if(j == n2){for(; i < n1; ++ i){objary[k] = leftary[i];++ k;}}free(leftary);free(rightary);leftary = NULL;rightary = NULL;
}
void merge_sort(int * objary,unsigned int index_start,unsigned int index_end)
{unsigned int index_middle;if(index_start < index_end){index_middle = (index_start + index_end) / 2;merge_sort(objary,index_start,index_middle);merge_sort(objary,index_middle + 1,index_end);merge(objary,index_start,index_middle,index_end);}
}
bool is_number_in_array(int array[],int number,int length){int start = 0;int end = length - 1;int half = (start + end) / 2;while(end > start){if(number > array[half]){printf("start:%d,half:%d,end:%d\n",start,half,end);printf("%d,%d\n",array[half],number);start = half ;half = (start + end) / 2;}else if(number < array[half]){printf("start:%d,half:%d,end:%d\n",start,half,end);printf("%d,%d\n",array[half],number);end = half ;half = (start + end) / 2;}else{return true;}}return false;
}bool IS_num_sum_of_two_elements(int array[],int sum,int length){merge_sort(array,0,length - 1);for(int i = 0; i < length; i ++){int j = length - 1;int sum_value = array[i] + array[j];if(sum < sum_value){j -= 1;}else if(sum > sum_value){i += 1;}elsereturn true;}return false;
}int main() {int array[] = {3,41,52,26,38,57,9,49};int length = sizeof(array)/ sizeof(array[0]);if(IS_num_sum_of_two_elements(array,200,length - 1))printf("true\n");elseprintf("false\n");return 0;
}
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