[LintCode] Longest Increasing Continuous Subsequence

Problem 最长连续递增／递减子序列

Give an integer array，find the longest increasing continuous subsequence in this array.
An increasing continuous subsequence:
Can be from right to left or from left to right.
Indices of the integers in the subsequence should be continuous.

Example

For [5, 4, 2, 1, 3], the LICS is [5, 4, 2, 1], return 4.
For [5, 1, 2, 3, 4], the LICS is [1, 2, 3, 4], return 4.

Note

设置正向计数器，后一位增加则计数器加1，否则置1。反向计数器亦然。
每一次比较后将较大值存入max。

Solution

O(1) space, O(n) time

public class Solution {
    public int longestIncreasingContinuousSubsequence(int[] A) {
        if (A == null || A.length == 0) return 0;
        int n = A.length;
        int count = 1, countn = 1, max = 1;
        int i = 1;
        while (i != n) {
            if (A[i] >= A[i-1]) {
                count++;
                countn = 1;
                max = Math.max(max, count);
            }
            else {
                countn++;
                count = 1;
                max = Math.max(max, countn);
            }
            i++;
        }
        return max;
    }
}

DP using two dp arrays, O(n) space

public class Solution {
    public int longestIncreasingContinuousSubsequence(int[] A) {
        if (A == null || A.length == 0) return 0;
        int n = A.length;
        if (n == 1) return 1;
        int[] dp = new int[n];
        int[] pd = new int[n];
        int maxdp = 0, maxpd = 0;
        dp[0] = 1;
        for (int i = 1; i < n; i++) {
            dp[i] = A[i] >= A[i-1] ? dp[i-1]+1 : 1;
            maxdp = Math.max(maxdp, dp[i]);
        }
        pd[n-1] = 1;
        for (int i = n-2; i >= 0; i--) {
            pd[i] = A[i] >= A[i+1] ? pd[i+1]+1 : 1;
            maxpd = Math.max(maxpd, pd[i]);
        }
        return Math.max(maxdp, maxpd);
    }
}

DP using one dp arrays, O(n) space

public class Solution {
    public int longestIncreasingContinuousSubsequence(int[] A) {
        if (A == null || A.length == 0) return 0;
        int n = A.length;
        if (n == 1) return 1;
        int[] dp = new int[n];
        int maxdp = 0, maxpd = 0;
        dp[0] = 1;
        for (int i = 1; i < n; i++) {
            dp[i] = A[i] >= A[i-1] ? dp[i-1]+1 : 1;
            maxdp = Math.max(maxdp, dp[i]);
        }
        for (int i = 1; i < n; i++) {
            dp[i] = A[i] <= A[i-1] ? dp[i-1]+1 : 1;
            maxpd = Math.max(maxpd, dp[i]);
        }
        return Math.max(maxdp, maxpd);
    }
}