941. Valid Mountain Array

原创于 2018-11-18 17:37:06 发布 · 210 阅读

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本文介绍了一种算法，用于判断一个整数数组是否为有效的山脉数组。有效山脉数组需满足长度大于等于3，且存在一个转折点，使数组在该点前递增，在该点后递减。文章通过示例详细解释了这一概念，并提供了实现这一功能的Java代码。

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Given an array A of integers, return true if and only if it is a valid mountain array.

Recall that A is a mountain array if and only if:

A.length >= 3
There exists some i with 0 < i < A.length - 1 such that:
- A[0] < A[1] < ... A[i-1] < A[i]
- A[i] > A[i+1] > ... > A[B.length - 1]

Example 1:Input: [2,1] Output: false

Example 2:Input: [3,5,5] Output: false

Example 3:Input: [0,3,2,1] Output: true

Note:

0 <= A.length <= 10000
0 <= A[i] <= 10000

public boolean validMountainArray(int[] A) {
        if (A.length < 3) return false;
        int pre = A[0];
        boolean decrease = false;
        boolean increase = false;
        for (int i = 1; i < A.length; i++) {
            if (A[i] == pre) {
                return false;
            }
            if (A[i] > pre && !decrease) {
                pre = A[i];
                increase = true;
                continue;
            } else {
                decrease = true;
                if (A[i] < pre) {
                    pre = A[i];
                    continue;
                } else {
                    return false;
                }
            }
        }
        return decrease&increase;
    }