C++二分查找算法演示代碼

#include <cstdio>
/*


傳統的二分查找，數組有序且沒有重復
/
int binary_S(int a, int n, int key)
{
 int l = 0, r = n-1;
 int mid;
 while (l <= r){
 mid = (l + r) >> 1;
 if (a[mid] == key)
     return mid;
 if (a[mid] > key)
     r = mid - 1;
 else
     l = mid + 1;

 }
 return -1;
}
/*
找出等于key且下標最小的值的下標，輸入數組有序
/
int binary_S2(int a, int n, int key)
{
 int l = 0, r = n-1;
 while (l < r){
 int mid = (l + r) >> 1;
 if (a[mid] >= key)
     r = mid;
 else
     l = mid + 1;

 }
 if (a[r] == key)
 return r;

 return -1;
}
/*
找出等于key且下標最大的值的下標，輸入數組有序
/
int binary_S3(int a, int n, int key)
{
 int l = 0, r = n-1;
 while (l < r){
 int mid = (l + r + 1) >> 1;
 if (a[mid] <= key)
     l = mid;
 else
     r = mid - 1;

 }
 if (a[l] == key)
 return l;

 return -1;
}
/*
找出一個先遞增后遞減數列的最大值
/
int binary_S4(int a, int n)
{
 int l = 0, r = n-1;
 int mid;
 while (l <= r){
 mid = (l + r) >> 1;
 if (mid > 0 && a[mid-1] > a[mid])
     r = mid - 1;
 else if (mid < n-1 && a[mid+1] > a[mid])
     l = mid + 1;
 else
     return a[mid];

 }
}</pre>