Given an array of integers, find if the array contains any duplicates. Your function
should return true if any value appears at least twice in the array, and it should
return false if every element is distinct.
用一个set存放数组元素,如果元素不能add,则返回true;
public boolean containsDuplicate(int[] nums) {
if(nums==null||nums.length<=0)
return false;
HashSet<Integer> set=new HashSet<Integer>();
for(int i:nums){
if(!set.add(i))
return true;
}
return false;
}