162. 寻找峰值——二分查找

class Solution {
public:
    int findPeakElement(vector& nums) {
        //局部肯定有序，当不存在峰值时，数组必定升序或降序
        int n = nums.size();
        if(n == 1 || nums[0] > nums[1])
            return 0;
        if(nums[n - 1] > nums[n - 2])
            return n - 1;
        int left = 0, right = n - 1, mid;
        while(left <= right){
            mid = (left + right) / 2;
            if(nums[mid] > nums[mid - 1] && nums[mid] > nums[mid + 1]){
                break;
            }
            else if(nums[mid] > nums[mid - 1]){
                left = mid + 1; //向右不会触碰到最右边，所以可以 + 1
            }
            else{
                right = mid;    //如果这里 - 1，则可能会碰到最左边，导致上面的if中超出边界
            }
        }
        return mid;
    }
};

Accepted
63/63 cases passed (0 ms)
Your runtime beats 100 % of cpp submissions
Your memory usage beats 63.44 % of cpp submissions (8.6 MB)