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a_376.java
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30 lines (29 loc) · 1.17 KB
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package dynamicProgramming;
/**
* 摆动序列
*/
public class a_376 {
public int wiggleMaxLength(int[] nums) {
/*
用up[i]和down[i]分别记录到第i个元素为止以上升沿和下降沿结束的最长“摆动”
序列长度，遍历数组，如果nums[i]>nums[i-1]，表明第i-1到第i个元素是上升的，
因此up[i]只需在down[i-1]的基础上加1即可，而down[i]保持down[i-1]不变；
如果nums[i]<nums[i-1]，表明第i-1到第i个元素是下降的，因此down[i]
只需在up[i-1]的基础上加1即可，而up[i]保持up[i-1]不变；如果nums[i]==nums[i-1]，
则up[i]保持up[i-1]，down[i]保持down[i-1]。比较最终以上升沿和下降沿结束的
最长“摆动”序列长度即可获取最终结果
*/
if (nums == null || nums.length == 0) {
return 0;
}
int up = 1, down = 1;
for (int i = 1; i < nums.length; i++) {
if (nums[i] > nums[i-1]) {
up = down + 1;
} else if (nums[i] < nums[i-1]) {
down = up + 1;
}
}
return Math.max(up, down);
}
}