LC1893-检查是否区域内所有整数都被覆盖

1893. 检查是否区域内所有整数都被覆盖

法1：时间复杂度\(O(n^2)\)

先暴力标记每个位置是否被覆盖，再检查目标区间

const int N = 55;
bool st[N];
class Solution {
public:
    bool isCovered(vector<vector<int>>& ranges, int left, int right) {
        memset(st,0,sizeof st);
        for(auto& e : ranges)
            for(int i = e[0]; i <= e[1]; ++i)st[i] = true;
        for(int i = left; i <= right; ++i)if(!st[i])return false;
        return true;
    }
};

法2：时间复杂度\(O(n)\)

利用差分快速操作某一段区间。

const int N = 55;
int diff[N];
class Solution {
public:
    bool isCovered(vector<vector<int>>& ranges, int left, int right) {
        memset(diff, 0, sizeof diff);
        int sum = 0;
        for(auto& e : ranges) ++ diff[e[0]], -- diff[e[1] + 1];
        for(int i = 0; i <= 50; ++i, sum += diff[i])
            if(i >= left && i <= right && sum <= 0)return false;
        return true;
    }
};