力扣第 198 场周赛部分题解

力扣第 198 场周赛部分题解

class Solution {
public:
    int numWaterBottles(int numBottles, int numExchange) {
        int a = 0,b = 0;
        int sum = 0;
        sum+=numBottles;
        while (numBottles >= numExchange)
        {
            a = (numBottles) / numExchange;
            sum += a;
            numBottles = (numBottles) % numExchange + a;
        }
        return sum;
    }
};

class Solution {
    String labels;
    TreeSet[] graph;
    int[] ans;

public int[] countSubTrees(int n, int[][] edges, String labels) {
    this.labels = labels;
    graph = new TreeSet[n];
    for (int i = 0; i < n; i++) {
        graph[i] = new TreeSet<>();
    }
    for (int[] edge : edges) {
        graph[edge[0]].add(edge[1]);
        graph[edge[1]].add(edge[0]);
    }
    ans = new int[n];
    dfs(0, new boolean[n]);
    return ans;
}

int[] dfs(int root, boolean[] visited) {
    visited[root] = true;
    //以root为根节点的子树中每个字母的个数
    int[] count = new int[26];
    //先统计根节点
    count[labels.charAt(root) - 'a']++;
    for (int next : graph[root]) {
        if (!visited[next]) {
            //再统计每个子树
            int[] res = dfs(next, visited);
            for (int i = 0; i < 26; i++) {
                count[i] += res[i];
            }
        }
    }
    //更新结果数组
    ans[root] = count[labels.charAt(root)-'a'];
    return count;
}
}

class Solution {
    int [] res;
    int [] arr;
    public int closestToTarget(int[] arr, int target) {
        res = new int [4 * arr.length];
        this.arr = arr;
        build_tree(0,arr.length-1,0);
        int n =arr.length;
        int l = 0;
        int r = 0;
        int t = Math.abs(-1000000000 + target);
        while(l < n && r < n){
            int tmp = query(0,n-1,l,r++,0);
            t = Math.min(t, Math.abs(tmp - target));
            if(tmp < target){
                while(tmp < target && l < r){
                    l++;
                    tmp = query(0,n-1,l,r,0);
                    t = Math.min(t, Math.abs(tmp - target));
                }
            }
        }return t;
    }
    void build_tree(int left,int right,int index)
    {
        if(left>=right)
        {
            res[index] = arr[left];
            return;
        }
        int mid = (left + right)/2;
        int left_index = index *2 + 1;
        int right_index = index * 2 + 2;
        build_tree(left,mid,left_index);
        build_tree(mid+1,right,right_index);
        res[index] = res[right_index]&res[left_index];
    }
    int query(int left,int right,int L,int R,int index)
    {
        if(L<=left&&R>=right)
            return res[index];
        if(L>right||left>R)
            return Integer.MAX_VALUE;
        int sum = query(left,(left+right)/2,L,R,index*2+1);
        sum = sum & query((left+right)/2 + 1,right,L,R,index*2+2);
        return sum;
    }
}