阿翰刷题系列 之 入门 1/14

package Day14.no1;



public class 二分查找 {
    public static void main(String[] args) {
        int[] nums = {-1,0,3,5,9,12};
        int target = 9;
        int[] nums2 = {-1,0,3,5,9,12};
        int target2 = 2;
        二分查找 s = new 二分查找();

        int search = s.search(nums, target);
        int search2 = s.search(nums2, target2);
        System.out.println(search);
        System.out.println(search2);
    }
    public int search(int[] nums, int target) {
        int l = 0;
        int r = nums.length - 1;

        while(l <= r){
            int mid = (l + r)/2;
            if(target == nums[mid]){
                return mid;
            }
            if (target > nums[mid] ){
                l = mid + 1;
            }else{
                r = mid - 1;
            }
        }
        return -1;
    }
}

left + right 容易溢出 left + (right - left) / 2就不会，(8 + 9) / 2 8 + (9 - 8) / 2 区别还是很大的！！

package Day14.no1;


public class _278 {
    public static void main(String[] args) {
        _278 s = new _278();
        System.out.println(s.firstBadVersion(5, 4));
        System.out.println(s.firstBadVersion(3, 1));
        System.out.println(s.firstBadVersion(4, 1));
        System.out.println(s.firstBadVersion(2126753390 , 1702766719));
    }
    public int firstBadVersion(int n, int bad) {
        int l = 0;
        int r = n;
        int mid;
        while(l= bad)
            return true;
        return false;
    }
}

package Day14.no1;


public class _35 {
    public static void main(String[] args) {
        int[] nums = {1,3,5,6};
        int target = 5;
        int target2 = 7;
        _35 s = new _35();

        int search = s.searchInsert(nums, target);
        int search2 = s.searchInsert(nums, target2);
        System.out.println(search);
        System.out.println(search2);
    }
    public int searchInsert(int[] nums, int target) {
        int l = 0, r = nums.length - 1,mid;
        while(l<=r){
            mid = l + (r - l) / 2;
            if (target == nums[mid]){
                return mid;
            }
            if(target < nums[mid]){
                r = mid - 1;
            }else {
                l = mid + 1;
            }
        }
        return l;
    }
}

主要是学到了 mid 不要写成 (l+r)/2