Java基础进阶_6

案例：输入一个字符串，统计每个字符出现的次数。

public class CountDemo {

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.print("请输入字符串：");
        String str = s.nextLine();

        Map<Character,Integer> res = new HashMap<>();

        for (int i = 0; i < str.length(); i++) {
            if (res.containsKey(str.charAt(i))){
                res.put(str.charAt(i),res.get(str.charAt(i)) + 1);
            } else {
                res.put(str.charAt(i),1);
            }
        }
        System.out.println(res);
    }
}

 二分查找：

public class HalfSearch {
    public static void main(String[] args) {
        int[] nums = new int[]{21,22,32,35,38,54,64,94,99,500};
        int index = halfSearch(nums, 54);
        System.out.println(index);
    }
    private static int halfSearch(int[] nums,int num) {
        int start = 0;
        int end = nums.length;
        while (start <= end){
            int middleIndex = (start+end)/2;
            if (num < nums[middleIndex]){
                end = middleIndex - 1;
            }else if (num > nums[middleIndex]){
                start = middleIndex + 1;
            }else {
                return middleIndex;
            }
        }
        return -1;
    }
}

 冒泡排序：

public class Bubbling {
    public static void main(String[] args) {
        int[] nums = new int[]{12,15,61,13,41,95,24,65,5,44};
        for (int i = 0; i < nums.length-1; i++){
            for (int j = 0; j < nums.length-i-1; j++) {
                if (nums[j]>nums[j+1]){
                    int temp = nums[j];
                    nums[j] = nums[j+1];
                    nums[j+1] = temp;
                }
            }
        }
        System.out.println(Arrays.toString(nums));
    }
}

选择排序：

public class Selection {
    public static void main(String[] args) {
        int[] nums = new int[]{12,15,61,13,41,95,24,65,5,44};
        for (int i = 0; i < nums.length-1; i++) {
            for (int j = i+1; j < nums.length; j++) {
                if (nums[j]<nums[i]){
                    int current = nums[j];
                    nums[j] = nums[i];
                    nums[i] = current;
                }
            }
        }
        System.out.println(Arrays.toString(nums));
    }
}