算法基础-二分查找

左闭右闭 [ left，right ]        [1,1]可以    

while( left <= right )        
        if( a[mid] > target )
                right = mid - 1
        else if( a[mid] < target )
                left = mid + 1

左闭右开 [ left，right )        [1，1)不可以

while( left < right )        
        if( a[mid] > target )        已经>target，开区间right = mid
                right = mid
        else if( a[mid] < target )
                left = mid + 1

public class Main {public static void main(String[] args) {Scanner in = new Scanner(System.in);int n = in.nextInt();int m = in.nextInt();int l, r;int[] a = new int[n];for(int i = 0; i < n; i ++)a[i] = in.nextInt();while(m -- > 0) {int first = -1, last = -1;int x = in.nextInt();l = 0;r = n - 1;while(l <= r) {int mid = (l + r) / 2;if(a[mid] > x) {r = mid - 1;} else if(a[mid] < x) {l = mid + 1;} else {first = mid;r = mid - 1;}}l = 0;r = n - 1;while(l <= r) {int mid = (l + r) / 2;if(a[mid] > x) {r = mid - 1;} else if(a[mid] < x) {l = mid + 1;} else {last = mid;l = mid + 1;}}System.out.println(first + " " + last);}}
}