LeetCode374. Guess Number Higher or Lower猜数 #算法# 第十三周

原题

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 lower1 : My number is higher0 : Congrats! You got it!

Example :

Input: n = 10, pick = 6
Output: 6

思路

最直接的方法是遍历1-n所有数，但这样明显效率不高，而且没有充分利用到guess函数反馈的信息。容易想到用二分查找法，根据guess的结果判断出所猜数的上下界，每次猜中间的数，就可以将其区间减少一半。类似的，也可以分成三份来划分区间。这里只用二分的方法。

代码

// Forward declaration of guess API.
// @param num, your guess
// @return -1 if my number is lower, 1 if my number is higher, otherwise return 0
int guess(int num);class Solution {
    
public:int guessNumber(int n) {
    int low = 1;int high = n;while(low <= high){
    int myGuess = low + (high - low) / 2;int res = guess(myGuess);if(res == 0) return myGuess;if(guess(myGuess) == 1){
     low = myGuess + 1;}else{
    high = myGuess - 1;}}}
};