update comments for 376

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_376.java

@@ -5,6 +5,16 @@ public class _376 {
     public static class Solution1 {
         /**
          * credit: https://leetcode.com/problems/wiggle-subsequence/discuss/84843/Easy-understanding-DP-solution-with-O(n)-Java-version
+         * <p>
+         * For every position in the array, there are only three possible statuses for it.
+         * <p>
+         * up position, it means nums[i] > nums[i-1]
+         * down position, it means nums[i] < nums[i-1]
+         * equals to position, nums[i] == nums[i-1]
+         * So we can use two arrays up[] and down[] to record the max wiggle sequence length so far at index i.
+         * If nums[i] > nums[i-1], that means it wiggles up. the element before it must be a down position. so up[i] = down[i-1] + 1; down[i] keeps the same with before.
+         * If nums[i] < nums[i-1], that means it wiggles down. the element before it must be a up position. so down[i] = up[i-1] + 1; up[i] keeps the same with before.
+         * If nums[i] == nums[i-1], that means it will not change anything becasue it didn't wiggle at all. so both down[i] and up[i] keep the same.
          */
         public int wiggleMaxLength(int[] nums) {
             int len = nums.length;