443.Two Sum - Greater than target

1.Description(Medium)

Given an array of integers, find how many pairs in the array such that their sum is bigger than a specific target number. Please return the number of pairs.

Example

Given numbers =[2, 7, 11, 15], target =24. Return1. (11 + 15 is the only pair)

Challenge

Do it in O(1) extra space and O(nlogn) time.

2.Code

跟609相似

 public int twoSum2(int[] nums, int target) {
        if(nums==null || nums.length<2){
            return 0;
        }
        Arrays.sort(nums);
        int head=0;
        int tail=nums.length-1;
        int result=0;
        while(head<tail){
            int sum=nums[head]+nums[tail];
            if(sum>target){
                result=result+(tail-head);
                tail--;
            }else{
                head++;
            }
        }
        return result;
    }