We are playing the Guess Game. The game is as follows:
I pick a number from 1 to n. You have to guess which number I picked.
Every time you guess wrong, I'll tell you whether the number is higher or lower.
You call a pre-defined API guess(int num)
which returns 3 possible results (-1
, 1
, or 0
):
-1 : My number is lower 1 : My number is higher 0 : Congrats! You got it!
Example:
n = 10, I pick 6. Return 6.
题意:
猜数字,有一个内置的函数guess,如果目标数字大于我们猜的,就返回1,小于则返回-1,相等就返回0.
思路:
二分法。设置l和r,初始值分别为1,n。不取0是因为题目说明1-n,并且注意题目说的my number是指目标数字。
代码:
/* The guess API is defined in the parent class GuessGame. @param num, your guess @return -1 if my number is lower, 1 if my number is higher, otherwise return 0 int guess(int num); */ public class Solution extends GuessGame { public int guessNumber(int n) { int l=1,r=n; while(l<=r) { int t=l+(r-l)/2; if(guess(t)==1) l=t+1; else if(guess(t)==-1) r=t-1; else return t; } return -1; } }