第一题

给定01数组和一个数字k，选择k个为0的数字变成1，使得连续出现的1的个数最多
用的暴力回溯

    static int res = Integer.MIN_VALUE;

    public static int GetMaxConsecutiveOnes (int[] nums, int k) {
        // write code here
        dfs(nums,k,0);
        return res == Integer.MIN_VALUE? -1 : res;
    }

    private static void dfs(int[] nums,int k,int idx){
        if(idx == k + 1){
            return;
        }
        int n = nums.length;
        for(int i = 0;i < n;i++) {
            int tmp = 0;
            while (i < n && nums[i] == 1) {
                tmp++;
                i++;
            }
            res = Math.max(res, tmp);
        }
        for (int i = 0; i < n; i++) {
            if(nums[i] == 0){
                nums[i] = 1;
                dfs(nums,k,idx+1);
                nums[i] = 0;
            }
        }
    }

第二题

螺旋矩阵，Leetcode的原题

    public static int[] SpiralMatrix (int[][] matrix) {
        // write code here
        int top = 0,left = 0;
        int rows = matrix.length,cols = matrix[0].length;
        int a = rows,b = cols;
        List<Integer> res = new ArrayList<>();
        int i = 0;
        while(top < rows && left < cols){
            while(left < cols){
                res.add(matrix[top][left]);
                left++;
            }
            left--;
            top++;
            while(top < rows){
                res.add(matrix[top][left]);
                top++;
            }
            top--;
            left--;
            if(res.size() == a * b)
                break;
            while(left >=i){
                res.add(matrix[top][left]);
                left--;
            }
            left++;
            top--;
            while(top > i){
                res.add(matrix[top][left]);
                top--;
            }
            top++;
            left++;
            rows--;
            cols--;
            i++;
        }
        int[] ans = new int[res.size()];
        int j = 0;
        for (Integer re : res) {
            ans[j++] = re;
        }
        return ans;
    }

第三题

字符串碎片的平均长度

    public static int GetFragment (String str) {
        // write code here
        if(str.length() == 0)
            return 0;
        List<Integer> list = new ArrayList<>();
        StringBuilder sb = new StringBuilder(str);
        sb.append('!');
        for (int i = 1; i < sb.length(); i++) {
            int cnt = 1;
            while(sb.charAt(i-1) == sb.charAt(i)){
                cnt+=1;
                i++;
            }
            list.add(cnt);
        }
        System.out.println(list);
        long sum = 0;
        for (Integer val : list) {
            sum += val;
        }
        return (int)sum/list.size();
    }