二分查找(等于x，小于x，小于等于x，大于x，大于等于x )
//等于x
//小于x
//小于等于x
//大于x
//大于等于x
1 #include <cstdio> 2 #include <cstdlib> 3 #include <cmath> 4 #include <cstring> 5 #include <string> 6 #include <set> 7 #include <map> 8 #include <list> 9 #include <stack> 10 #include <queue> 11 #include <vector> 12 #include <algorithm> 13 #include <iostream> 14 using namespace std; 15 #define ll long long 16 #define minv 1e-6 17 #define inf 1e9 18 const long maxn=1e5+5; 19 const ll mod=1e9+7; 20 21 //µÈÓÚx 22 //СÓÚx 23 //СÓÚµÈÓÚx 24 //´óÓÚx 25 //´óÓÚµÈÓÚx 26 27 long a[maxn]; 28 29 int main() 30 { 31 long n,s,i,l,r,m; 32 scanf("%ld",&n); 33 for (i=1;i<=n;i++) 34 scanf("%ld",&a[i]); 35 scanf("%ld",&s); 36 l=1; r=n; 37 while (l<=r) 38 { 39 m=(l+r)>>1; 40 if (a[m]>=s) //a[l]>=s 41 r=m-1; //a[r]<s 42 else 43 l=m+1; 44 } 45 printf("%ld\n",a[l]); 46 printf("%ld\n",a[r]); 47 /* 48 8 1 1 1 4 4 6 6 6 49 0 50 1 0 51 52 8 1 1 1 4 4 6 6 6 53 10 54 0 6 55 56 8 1 1 1 4 4 6 6 6 57 4 58 4 1 59 60 61 8 1 1 1 4 4 6 6 6 62 3 63 4 1 64 65 8 1 1 1 4 4 6 6 6 66 5 67 6 4 68 69 70 71 72 */ 73 return 0; 74 }
a[l]>s a[r]<=s
1 #include <cstdio> 2 #include <cstdlib> 3 #include <cmath> 4 #include <cstring> 5 #include <string> 6 #include <set> 7 #include <map> 8 #include <list> 9 #include <stack> 10 #include <queue> 11 #include <vector> 12 #include <algorithm> 13 #include <iostream> 14 using namespace std; 15 #define ll long long 16 #define minv 1e-6 17 #define inf 1e9 18 const long maxn=1e5+5; 19 const ll mod=1e9+7; 20 21 //µÈÓÚx 22 //СÓÚx 23 //СÓÚµÈÓÚx 24 //´óÓÚx 25 //´óÓÚµÈÓÚx 26 27 long a[maxn]; 28 29 int main() 30 { 31 long n,s,i,l,r,m; 32 scanf("%ld",&n); 33 for (i=1;i<=n;i++) 34 scanf("%ld",&a[i]); 35 scanf("%ld",&s); 36 l=1; r=n; 37 while (l<=r) 38 { 39 m=(l+r)>>1; 40 if (a[m]>s) //a[l]>s 41 r=m-1; //a[r]<=s 42 else 43 l=m+1; 44 } 45 printf("%ld\n",a[l]); 46 printf("%ld\n",a[r]); 47 /* 48 8 1 1 1 4 4 6 6 6 49 0 50 1 0 51 52 8 1 1 1 4 4 6 6 6 53 10 54 0 6 55 56 8 1 1 1 4 4 6 6 6 57 4 58 6 4 59 60 61 8 1 1 1 4 4 6 6 6 62 3 63 4 1 64 65 8 1 1 1 4 4 6 6 6 66 5 67 6 4 68 69 70 71 72 */ 73 return 0; 74 }
若要判断相等，则
Code1 ： if l!=n+1 && a[l]==s
Code2 ： if r!=0 && a[r]==s
