Q:
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.
A:
没什么想的,就是取中间值,然后对比/* 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) { return helper(1,n); } private int helper(int a, int b){ if(a==b) return a; int mid = a + (b-a)/2; int res = guess(mid); if(res == 0) return mid; if(res == 1) return helper(mid+1,b); // res == 1, mine is bigger return helper(a,mid-1); } }
Learned:
1: guess(int num) return -1, mean my target number is lower than your given num这个是题意理解反了。2: 求mid的时候, 以前还记得,刚刚忘了(主要是LC一直没考虑这种情况), 要写成
int mid = a + (b-a)/2;
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