算法类

双指针

two sum

• 有序数组中查找和为 target 的索引+1数组

twoSum

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        if (numbers == null || numbers.length == 0) {
            return null;
        }
        int startIndex = 0;
        int lastIndex = numbers.length - 1;
        int sum = 0;
        for (int i = 0; i < numbers.length; i++) {
            sum = numbers[startIndex] + numbers[lastIndex];
            if (sum < target) {
                    startIndex++;
            } else if (sum > target) {
                lastIndex--;
            } else {
                return new int[]{startIndex+1, lastIndex+1};
            }
        }
        return null;
    }
}

平方数之和

平方数之和

• 二分法

• 双指针

  class Solution {
    public boolean judgeSquareSum(int c) {
        if (c < 0) {
            return false;
        }
        int first = 0;
        int last = (int)Math.sqrt(c);
        int sum = 0;
        while (first <= last) {
            sum = first * first + last * last;
            if (sum < c) {
                first++;
            } else if (sum > c) {
                last--;
            } else {
                return true;
            }
        }
        return false;
    }
  }

反转字符串中的元音字母

• 注意元音字母有大写
• 是元音和元音的反转

• 左右指针往中间查找

  • 注意 continue 的使用 ```java class Solution { public String reverseVowels(String s) { char[] result = s.toCharArray(); int first = 0; int last = s.length()-1; char firstCh; char lastCh; char temp; while (first < last) {

       firstCh = result[first];
       lastCh = result[last];
       if (!isVowel(firstCh)) {
           first++;
           continue;
       } 
       if (!isVowel(lastCh)) {
           last--;
           continue;
       } 
       temp = result[first];
       result[first] = result[last];
       result[last] = temp;
       first++;
       last--;

    } return new String(result); }

    private boolean isVowel(char c) { switch (c) {

       case 'a':
       case 'A':
       case 'e':
       case 'E':
       case 'i':
       case 'I':
       case 'o':
       case 'O':
       case 'u':
       case 'U':
           return true;
       default:
           return false;

    } }

} ```