456. 132 Pattern
Given an array of n
integers nums
, a 132 pattern is a subsequence of three integers nums[i]
, nums[j]
and nums[k]
such that i < j < k
and nums[i] < nums[k] < nums[j]
.
Return true
if there is a 132 pattern in nums
, otherwise, return false
.
Follow up: The O(n^2)
is trivial, could you come up with the O(n logn)
or the O(n)
solution?
Example 1:
Input: nums = [1,2,3,4] Output: false Explanation: There is no 132 pattern in the sequence.
Example 2:
Input: nums = [3,1,4,2] Output: true Explanation: There is a 132 pattern in the sequence: [1, 4, 2].
Example 3:
Input: nums = [-1,3,2,0] Output: true Explanation: There are three 132 patterns in the sequence: [-1, 3, 2], [-1, 3, 0] and [-1, 2, 0].
Constraints:
n == nums.length
1 <= n <= 104
-109 <= nums[i] <= 109
Rust Solution
struct Solution;
use std::i32;
impl Solution {
fn find132pattern(nums: Vec<i32>) -> bool {
let n = nums.len();
let mut a3 = i32::MIN;
let mut stack: Vec<i32> = vec![];
for i in (0..n).rev() {
if nums[i] < a3 {
return true;
} else {
while let Some(top) = stack.pop() {
if nums[i] > top {
a3 = top;
} else {
stack.push(top);
break;
}
}
}
stack.push(nums[i]);
}
false
}
}
#[test]
fn test() {
let nums = vec![1, 2, 3, 4];
let res = false;
assert_eq!(Solution::find132pattern(nums), res);
let nums = vec![3, 1, 4, 2];
let res = true;
assert_eq!(Solution::find132pattern(nums), res);
let nums = vec![-1, 3, 2, 0];
let res = true;
assert_eq!(Solution::find132pattern(nums), res);
}
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