二分查找Review
- 先從大到小排序,再查找。
- 查找 對應 索引值。
- 有個公式可能要注意一下。
low+2(high−low)
#include <stdio.h>
void swap(int *a, int *b){
*a = *a ^ *b;
*b = *a ^ *b;
*a = *a ^ *b;
}
int find_value(int x[], int k, int n){
int low = 0;
int high = n - 1;
int mid_index;
while(low <= high){
mid_index = low + (high - low)/2;
if(x[mid_index] < k){
high = mid_index - 1;
}
else if(x[mid_index] > k){
low = mid_index + 1;
}
else{
return mid_index + 1;
}
}
return -1;
}
int main(){
int arr[10] = {2,3,41,412,421,0,1,4,6,10};
int i, j;
for(i = 0; i < 9; i++){
int tag = i;
for(j = i + 1; j < 10; j++){
if(arr[tag] < arr[j]){
tag = j;
}
}
if(tag != i){
swap(&arr[tag], &arr[i]);
}
}
for(i = 0; i < 10; i++){
printf("%d ", arr[i]);
}
printf("\n");
int index = find_value(arr, 412, 10);
if(index == -1){
printf("Can't get the number's index.\n");
}
else{
printf("%d\n", index);
}
return 0;
}