O(n) 时间复杂度，题目说了肯定有解

public class Solution {
    public int MoreThanHalfNum_Solution(int [] array) {
        int res = 0, vote = 0;
        for (int i = 0; i < array.length; i ++ ) {
            if (vote == 0) {
                res = array[i];
                vote ++ ;
            } else if (res == array[i]) {
                vote ++ ;
            } else if (res != array[i]) {
                vote -- ;
            }
        }
        return res;
    }
}