# [LintCode] 3Sum Smaller

### Problem

Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.

### Example

Given nums = [-2,0,1,3], target = 2, return 2.

### Explanation:

Because there are two triplets which sums are less than 2:
[-2, 0, 1]
[-2, 0, 3]

### Challenge

Could you solve it in O(n2) runtime?

### Solution

``````public class Solution {
/**
* @param nums:  an array of n integers
* @param target: a target
* @return: the number of index triplets satisfy the condition nums[i] + nums[j] + nums[k] < target
*/
public int threeSumSmaller(int[] nums, int target) {
if (nums.length < 3) return 0;
Arrays.sort(nums);
if (nums[0] >= target) return 0;
int count = 0;
for (int i = 0; i < nums.length-2; i++) {
int start = i+1, end = nums.length-1;
int sum = target - nums[i];
while (start < end) {
if (nums[start] + nums[end] < sum) {
count += end-start;
start++;
} else {
end--;
}
}
}
return count;
}
}``````