L609 Two Sum V

Given an array of integers, find how many pairs in the array such that their sum isless than or equal toa specific target number. Please return the number of pairs.

Example

Given nums =[2, 7, 11, 15], target =24. Return5. 2 + 7 < 24 2 + 11 < 24 2 + 15 < 24 7 + 11 < 24 7 + 15 < 25

这题跟Two sumII很像，就是算res的条件有些不一样。

public int twoSum5(int[] nums, int target) {
    if (nums == null || nums.length == 0) {
        return 0;
    }

    int res = 0;
    Arrays.sort(nums);
    int left = 0;
    int right = nums.length - 1;
    while (left < right) {
        int sum = nums[left] + nums[right];
        if (sum <= target) {
            res += right - left;
            left++;
        } else {
            right--;
        }
    }

    return res;
}