Java算法 leetcode简单刷题记录7

最长奇偶子数组： https://leetcode.cn/problems/longest-even-odd-subarray-with-threshold/

有的题看着不难，根据提示往下写，有的case就是死活过不了
这道题耗了挺久…

class Solution {public int longestAlternatingSubarray(int[] nums, int threshold) {int max = 0;for (int i = 0; i < nums.length; i++) {for (int r = i; r < nums.length; r++) {if (isSatisfied(nums, threshold, i, r)) {max = Math.max(r - i + 1, max);}}}return max;}private static boolean isSatisfied(int[] nums, int threshold, int l, int r) {if (nums[l] % 2 != 0) {return false;}for (int i = l; i <= r; i++) {if (nums[i] > threshold || (i < r && nums[i] % 2 == nums[i + 1] % 2)) {return false;}}if (l == r && nums[l] <= threshold) {return true;}return true;}
}

统计和小于目标的下标对数目： https://leetcode.cn/problems/count-pairs-whose-sum-is-less-than-target/
直接写就行
爬楼梯： https://leetcode.cn/problems/climbing-stairs/

递归或者 n+1的数组；
n>=3时，f(n) = f(n-2) + f(n-1)
字典序最小回文串: https://leetcode.cn/problems/lexicographically-smallest-palindrome/

双指针俩边移动取最小的字符

class Solution {public String makeSmallestPalindrome(String s) {int left = 0;int right = s.length() - 1;char[] chars = s.toCharArray();while (left < right) {if (chars[left] < chars[right]) {chars[right] = chars[left];} else if (chars[left] > chars[right]) {chars[left] = chars[right];}++left;--right;}return new String(chars);}
}

使用最小花费爬楼梯： https://leetcode.cn/problems/min-cost-climbing-stairs/

动态规划

class Solution {public int minCostClimbingStairs(int[] cost) {int[] dp = new int[cost.length+1];dp[0] = 0;dp[1] = 0;for(int i =2;i<=cost.length;i++){dp[i] = Math.min(dp[i-1]+cost[i-1],dp[i-2]+cost[i-2]);}return dp[cost.length];}
}