ACM：二分查找，以及利用二分法来找上下界

int binary_search(int *array, int length, int key) {
int start = 0, end = length - 1;
while(end >= start) {
int middle = start + (end - start) / 2;
int tmp = array[middle];
if(tmp < key) start = middle + 1;
else if (tmp > key) end = middle - 1;
else return middle;
}
return -1;
}

#include<stdio.h>
#include<assert.h>

int A[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};

int bsearch(int* A, int x, int y, int v) {
int m;
while(x < y) {
m = x+(y-x)/2;
if(A[m] == v) return m;
else if(A[m] > v) y = m;
else x = m+1;
}
return -1;
}

int main() {
int i;
for(i = 1; i <= 11; i++)
assert(bsearch(A, 0, 11, i) == i-1);
printf("Ok!\n");
return 0;
}

#include<stdio.h>
#include<assert.h>
#include <iostream>
using namespace std;

int A[] = {1, 2, 3, 3, 3, 3, 3, 5, 6};

int lower_bound(int *array, int length, int v) {
int start = 0, end = length - 1;
while(start <= end) {
int middle = start + (end - start) / 2;
int tmp = array[middle];
if(array[middle] >= v) end = middle - 1;
else start = middle + 1;
}
return start;
}

int upper_bound(int *array, int length, int v) {
int start = 0, end = length-1;
while(start <= end) {
int middle = start + (end - start) / 2;
int tmp = array[middle];
if(array[middle] <= v) start = middle + 1;
else end = middle - 1;
}
return start;
}

int main() {
cout << lower_bound(A, 9, 3) << endl
<< upper_bound(A, 9, 3) << endl;
return 0;
}