Leetcode845 最长的山脉

 

　　JAVA 递归描述：

 　　int re = 0;

    public final int longestMountain(int[] arr) {
        if (arr.length < 3) return 0;
        longest(arr, 1, 0, 0);
        return re == 0 ? re : re + 1;
    }

    private final void longest(int[] arr, int end, int upLen, int downLen) {
        if (end == arr.length) {
            if (downLen > 0) re = Math.max(re, upLen + downLen);
            return;
        }
        if (arr[end - 1] < arr[end]) {
            if (downLen > 0) {
                re = Math.max(re, upLen + downLen + 1);
                longest(arr, end + 1, 0, 0);
            } else longest(arr, end + 1, upLen + 1, 0);
            return;
        }
        if (arr[end - 1] == arr[end]) {
            if (downLen > 0) re = Math.max(re, upLen + downLen);
            longest(arr, end + 1, 0, 0);
            return;
        }
        if (upLen > 0) {
            re = Math.max(re, upLen + downLen);
            longest(arr, end + 1, upLen, downLen + 1);
        } else longest(arr, end + 1, 0, 0);
    }

　　JS 递推描述：

/**
 * @param {number[]} arr
 * @return {number}
 */
var longestMountain = function (arr) {
    if ((!arr) || arr.length < 3) return 0;
    let up = 0, down = 0, re = 0;
    for (let i = 1; i < arr.length; i++) {
        if (arr[i] > arr[i - 1]) {
            if (down > 0) {
                re = Math.max(re,up + down + 1);
                up = 1;
                down = 0;
            } else up++;
            continue;
        }
        if (arr[i] == arr[i - 1]) {
            if (down > 0) {
                re = Math.max(re,up + down + 1);
                up = 0;
                down = 0;
            } else up = 0;
            continue;
        }
        if (up != 0) {
            down++;
            re = Math.max(re,up + down + 1);
        }
    }
    return re;
};