标签：increase 两种 col for NPU put code == turn
An array is monotonic if it is either monotone increasing or monotone decreasing.
An array A is monotone increasing if for all i <= j, A[i] <= A[j]. An array A is monotone decreasing if for all i <= j, A[i] >= A[j].
Return true if and only if the given array A is monotonic.
Example 1:
Input: [1,2,2,3]
Output: true
Example 2:
Input: [6,5,4,4]
Output: true
Example 3:
Input: [1,3,2]
Output: false
Example 4:
Input: [1,2,4,5]
Output: true
Example 5:
Input: [1,1,1]
Output: true
Note:
1 <= A.length <= 50000-100000 <= A[i] <= 100000
M1: two pass
一开始试图在one pass判断两种单调状态，但无法处理 {1, 1, 0}这样的情况，必须得two pass分别判断是单调增还是单调减，再把结果取或。需要遍历两次数组，不是最优。
时间：O(N)，空间：O(1)
class Solution { public boolean isMonotonic(int[] A) { return increasing(A) || decreasing(A); } private boolean increasing(int[] A) { for(int i = 0; i + 2 < A.length; i++) { if(A[i] <= A[i+1]) { if(A[i+1] > A[i+2]) return false; } else return false; } return true; } private boolean decreasing(int[] A) { for(int i = 0; i + 2 < A.length; i++) { if(A[i] >= A[i+1]) { if(A[i+1] < A[i+2]) return false; } else return false; } return true; } }
M2: one pass
在M1的基础上，用两个boolean变量表示增还是减。先把两个值都初始化为true。如果有元素递减，increase=false；如果有元素递增，decrease=false。最后返回increase或decrease
时间：O(N)，空间：O(1)
class Solution { public boolean isMonotonic(int[] A) { if(A.length == 1) return true; boolean increasing = true; boolean decreasing = true; for(int i = 0; i + 1 < A.length; i++) { if(A[i] < A[i+1]) decreasing = false; if(A[i] > A[i+1]) increasing = false; } return increasing || decreasing; } }
标签：increase 两种 col for NPU put code == turn
原文地址：https://www.cnblogs.com/fatttcat/p/10053530.html
