259. 3Sum Smaller
Given an array of n integers nums and an integer 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.
Follow up: Could you solve it in O(n2) runtime?
Example 1:
Input: nums = [-2,0,1,3], target = 2 Output: 2 Explanation: Because there are two triplets which sums are less than 2: [-2,0,1] [-2,0,3]
Example 2:
Input: nums = [], target = 0 Output: 0
Example 3:
Input: nums = [0], target = 0 Output: 0
Constraints:
n == nums.length0 <= n <= 300-100 <= nums[i] <= 100-100 <= target <= 100
Rust Solution
struct Solution;
impl Solution {
fn three_sum_smaller(mut nums: Vec<i32>, target: i32) -> i32 {
nums.sort_unstable();
let n = nums.len();
let mut res = 0;
for i in 0..n {
let mut j = i + 1;
let mut k = n - 1;
while j < k {
if nums[i] + nums[j] + nums[k] < target {
res += k - j;
j += 1;
} else {
k -= 1;
}
}
}
res as i32
}
}
#[test]
fn test() {
let nums = vec![-2, 0, 1, 3];
let target = 2;
let res = 2;
assert_eq!(Solution::three_sum_smaller(nums, target), res);
}
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