LeetCode 259: 3Sum Smaller Solution

Master LeetCode problem 259 (3Sum Smaller), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

259. 3Sum Smaller

Medium

Array Two Pointers Binary Search Sorting

Problem Explanation

Explanation:

This problem asks us to find the number of triplets in an array whose sum is less than a given target. We can solve this problem using a two-pointer approach.

Sort the array in non-decreasing order.
Initialize a count variable to 0.
Iterate over the array with a fixed index i and use two pointers left and right to find the pairs that sum up to less than the target.
If the sum of nums[i] + nums[left] + nums[right] is less than the target, then all the numbers between left and right form valid pairs as well.
Increment the count by right - left and move the left pointer to the right.
If the sum is greater than or equal to the target, decrement the right pointer.
Repeat steps 4-6 until the left pointer crosses the right pointer.
Return the final count.

: :

Solution Code

class Solution {
    public int threeSumSmaller(int[] nums, int target) {
        Arrays.sort(nums);
        int count = 0;
        for (int i = 0; i < nums.length - 2; i++) {
            int left = i + 1, right = nums.length - 1;
            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum < target) {
                    count += right - left;
                    left++;
                } else {
                    right--;
                }
            }
        }
        return count;
    }
}

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