二分搜尋

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// CodeForces 600B
//二分搜尋 時間複雜度為O(log n)
#include<stdio.h>#include<string.h>#include<stdlib.h>#include<ctype.h>#include<math.h>#include<algorithm>using namespace std;#define N 200100#define INF 0x3f3f3f3fint a[N], b[N];int main(){    int n, m;    scanf("%d%d", &n, &m);    for(int i=0; i<n; i++)        scanf("%d", &a[i]);    for(int i=0; i<m; i++)        scanf("%d", &b[i]);    sort(a, a+n);    for(int i=0; i<m; i++)    {        int left, right, mid=-1;        left=0, right=n-1;        while(left<=right)        {            mid=(left+right)/2;            if(a[mid]>b[i])            {                if(a[mid-1] <= b[i]) break;                right=mid-1;            }            else if(a[mid]<=b[i])            {                if(mid == n-1)                {                    mid ++;break;                }                left=mid+1;            }        }        printf("%d%c", mid, i==m-1 ? ‘\n‘ : ‘ ‘);    }    return 0;}

 

二分搜尋