LeetCode Monotonic Array【Easy】

• 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:

Example 5:

Input: [1,1,1]
Output: true

Note:

1. 1 <= A.length <= 50000
2. -100000 <= A[i] <= 100000

解决

该题主要是求给定一个数组，判断该数组是否是单调数组，这里给出两种解决方案，其中方案二为递归方法。

代码

常规方案

   /**
   *  常规方案
   * @param A
   * @return
   */
  public boolean isMonotonic(int[] A) {

      //ascStatus 递增 默认true
      //descStatus 递减 默认true
      boolean ascStatus = true;
      boolean descStatus = true;
      if (A.length == 1||A.length==0) {
          return true;
      }
      //循环内判断递增或者递减
      for (int i = 0; i < A.length - 1; i++) {
          if (A[i] < A[i + 1]) {
              ascStatus = false;
          }
          if (A[i] > A[i + 1]) {
              descStatus = false;
          }
      }
      return (ascStatus||descStatus);
  }

递归方案

 /**
   * 递归方案
   * @param A
   * @return
   */
  public boolean isMonotonic(int[] A) {
      int len = A.length;
      return isDecrease(A,len)||isIncrease(A,len);
  }
  /**
   * 递增判断  递归
   * @param A
   * @param len
   * @return
   */
  public boolean isIncrease(int[] A,int len){
      if(len==1){
          return true;
      }
      return (A[len-2]<=A[len-1]&&isIncrease(A,len-1));
  }

  /**
   * 递减判断 递归
   * @param A
   * @param len
   * @return
   */
  public boolean isDecrease(int[] A,int len){
      if(len==1){
          return true;
      }
      return (A[len-2]>=A[len-1]&&isDecrease(A,len-1));
  }