LeetCode知识点总结 - 941

LeetCode 941. Valid Mountain Array

题目

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

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

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

思路

先找到peak，检查peak是不是在第一位，再检查peak之后是不是递减的。

答案

public boolean validMountainArray(int[] A) {
        int N = A.length;
        int i = 0;

        // walk up
        while (i+1 < N && A[i] < A[i+1])
            i++;

        // peak can't be first or last
        if (i == 0 || i == N-1)
            return false;

        // walk down
        while (i+1 < N && A[i] > A[i+1])
            i++;

        return i == N-1;
    }

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来源： https://blog.csdn.net/m0_59773145/article/details/122632776