简单题过过瘾；突击学习，记忆为主，感觉至上，多看看实现好的数据结构，java方法

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class Solution {
    public boolean isThree(int n) {
        int cnt = 0;
        for (int i = 2; i < n; i++) {
            if ((n % i) == 0) {
                System.out.println(i);
                cnt++;
            }
        }
        System.out.println(cnt);
        return cnt == 1;
    }
}

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// 2000
public class reversePrefix {

    public static void main(String[] args) {
        System.out.println(reversePrefix("abcdefd", 'd'));
    }

    public static String reversePrefix(String word, char ch) {
        int i = word.indexOf(ch);
        String left = word.substring(0, i + 1);
        String right = word.substring(i + 1);
        return new StringBuilder(left).reverse().append(right).toString();
    }
}

2006. 差的绝对值为 K 的数对数目

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public class countKDifference2006 {

    public static void main(String[] args) {
        int i = countKDifference(new int[]{3,2,1,5,4}, 2);
        System.out.println(i);
    }

    public static int countKDifference(int[] nums, int k) {
        // 最简双指针
        int left = 0;
        int ans = 0;
        int len = nums.length;
        while (left < len) {
            int right = left + 1;
            while (right < len) {
                if (Math.abs(nums[left] - nums[right]) == k) {
                    ans += 1;
                }
                right++;
            }
            left++;
        }
        return ans;
    }
}

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class Solution {
    public int finalValueAfterOperations(String[] operations) {
       int x =0 ;
        for (String operation : operations) {
            switch (operation){
                case "X++":
                    ++x;
                    break;
                case "++X":
                    ++x;
                    break;
                case"X--":
                    --x;
                    break;
                case"--X":
                    --x;
                    break;
            }
        }
        return x;
    }
}

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头疼
2027. 转换字符串的最少操作次数

public class minimumMoves2027 {
    public static void main(String[] args) {
        System.out.println(minimumMoves("OXOX"));
    }

    public static int minimumMoves(String s) {
        int covered = -1, res = 0;
        for (int i = 0; i < s.length(); i++) {
            // X开头的地方可以覆盖后面的两个字符串，直接跳过
            if (s.charAt(i) == 'X' && i > covered) {
                res++;
                covered = i + 2;
            }
        }
        return res;
    }

}

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class Solution {
    public int alternatingSubarray(int[] nums) {
        // 双指针
        int left = 0;

        int ans = 0;
        while (left < nums.length) {
            int right = left;
            int res = 1;
            while (right < nums.length) {
                right++;
                if (right < nums.length && ((nums[right] - nums[left]) == (res % 2))) {
                     res++;
                }else {
                    ans  = Math.max(res,ans);
                    break;
                }
                if(right == (nums.length-1)){
                    ans  = Math.max(res,ans);
                }
            }
            left++;
        }
       return ans<2?-1:ans;
    }
}