Two Sum

Given an array of integers, find how many unique pairsin the array such that their sum is equal to a specific target number. Please return the number of pairs.

Have you met this question in a real interview? 

Yes

Example

Given nums = [1,1,2,45,46,46], target = 47
return 2

1 + 46 = 47
2 + 45 = 47

java

public class Solution {    /*     * @param nums: an array of integer     * @param target: An integer     * @return: An integer     */    public int twoSum6(int[] nums, int target) {        // write your code here        if (nums == null || nums.length == 0 || nums.length == 1) {            return 0;        }        int left = 0;        int right = nums.length - 1;        int value = 0;        int count = 0;        Arrays.sort(nums);        while (left < right) {            value = nums[left] + nums[right];            if (left < right && value < target) {                left++;            }            if (left < right && value > target) {                right--;            }            if (left < right && value == target) {                count++;                left++;                right--;                while (left < right && nums[left] == nums[left - 1]) {                    left++;                }                while (left < right && nums[right] == nums[right + 1]) {                    right--;                }            }        }        return count;    }}

python

class Solution:    """    @param: nums: an array of integer    @param: target: An integer    @return: An integer    """    def twoSum6(self, nums, target):        # write your code here        if nums == None or len(nums) == 0 or len(nums) == 1:            return 0        left, right, value, count = 0, len(nums) - 1, 0, 0        nums.sort()        while left < right:            value = nums[left] + nums[right]            if left < right and value < target:                left += 1            if left < right and value > target:                right -= 1            if left < right and value == target:                count += 1                left += 1                right -= 1                while left < right and nums[left] == nums[left - 1]:                    left += 1                while left < right and nums[right] == nums[right + 1]:                    right -= 1        return count