LeetCode 热题100道-Day10

颜色分类

• 只需要将前两种颜色归类好就行了，剩下

class Solution {
    public void sortColors(int[] nums) {
        int n = nums.length, i = 0, j = 0, temp = o, per = 0;
        for (; i < n; ++i) {
            if (nums[i] == 0) {
                temp = nums[i];
                nums[i] = nums[per];
                nums[per] = temp;
                ++per;
            }
        }
        for (j = per; j < n; ++j) {
            if (nums[j] == 1) {
                temp = nums[j];
                nums[j] = nums[per];
                nums[per] = temp;
                ++per;
            } 
        }
    }
}

最小覆盖子串

• 为了保证覆盖子集是唯一的，于是定义 check 进行确认

class Solution {
    Map<Character, Integer> ori = new HashMap<Character, Integer>();
    Map<Character, Integer> cnt = new HashMap<Character, Integer>();

    public String minWindow(String s, String t) {
        int tLen = t.length();
        for (int i = 0; i < tLen; i++) {
            char c = t.charAt(i);
            ori.put(c, ori.getOrDefault(c, 0) + 1);
        }
        int l = 0, r = -1;
        int len = Integer.MAX_VALUE, ansL = -1, ansR = -1;
        int sLen = s.length();
        while (r < sLen) {
            ++r;
            if (r < sLen && ori.containsKey(s.charAt(r))) {
                cnt.put(s.charAt(r), cnt.getOrDefault(s.charAt(r), 0) + 1);
            }
            while (check() && l <= r) {
                if (r - l + 1 < len) {
                    len = r - l + 1;
                    ansL = l;
                    ansR = l + len;
                }
                if (ori.containsKey(s.charAt(l))) {
                    cnt.put(s.charAt(l), cnt.getOrDefault(s.charAt(l), 0) - 1);
                }
                ++l;
            }
        }
        return ansL == -1 ? "" : s.substring(ansL, ansR);
    }

    public boolean check() {
        Iterator iter = ori.entrySet().iterator(); 
        while (iter.hasNext()) { 
            Map.Entry entry = (Map.Entry) iter.next(); 
            Character key = (Character) entry.getKey(); 
            Integer val = (Integer) entry.getValue(); 
            if (cnt.getOrDefault(key, 0) < val) {
                return false;
            }
        } 
        return true;
    }
}

子集

• 利用 << 左移来进行求解子集

class Solution {
    List<Integer> t = new ArrayList<Integer>();
    List<List<Integer>> ans = new ArrayList<List<Integer>>();

    public List<List<Integer>> subsets(int[] nums) {
        int n = nums.length, mask = 0;
        for (; mask < (1 << n); ++mask) {
            t.clear();
            for (int i = 0; i < n; ++i) {
                if ((mask & (1 << i)) != 0) {
                    t.add(nums[i]);
                }
            }
            ans.add(new ArrayList<Integer>(t));
        }
        return ans;
    }
}