題目描述：

https://leetcode-cn.com/problems/largest-number-at-least-twice-of-others/

Java程式碼：

class Solution {
    public int dominantIndex(int[] a) {
        int ans=0;
        for(int i=1;i<a.length;i++)if(a[ans]<a[i])ans=i;
        for(int e:a)if(a[ans]!=e&&a[ans]<e+e)return -1;
        return ans;
    }
}