LC 456. 132 Pattern

标签：check   whether   iss   bsp   fast   时间   memory   class   int   

Given a sequence of n integers a1, a2, ..., an, a 132 pattern is a subsequence ai, aj, ak such that i < j < k and ai < ak < aj. Design an algorithm that takes a list of n numbers as input and checks whether there is a 132 pattern in the list.

Note: n will be less than 15,000.

Example 1:

Input: [1, 2, 3, 4]

Output: False

Explanation: There is no 132 pattern in the sequence.

Example 2:

Input: [3, 1, 4, 2]

Output: True

Explanation: There is a 132 pattern in the sequence: [1, 4, 2].

Example 3:

Input: [-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].

class Solution {
public:
  bool find132pattern(vector<int>& nums) {
    int third = INT32_MIN;
    stack<int> s;
    for(int i=nums.size()-1; i>=0; i--) {
      if(nums[i] < third) return true;
      while(!s.empty() && nums[i] > s.top()) {
        third = s.top();
        s.pop();
      }
      s.push(nums[i]);
    }
    return false;
  }
};

LC 456. 132 Pattern

标签：check   whether   iss   bsp   fast   时间   memory   class   int   

原文地址：https://www.cnblogs.com/ethanhong/p/10355805.html