神经，树状数组做多了一开始还想着用树状数组来查询差分数组，但是我们要进行所有元素的查询，直接过一遍就好啦

class Solution { public:     int numberOfPoints(vector>& nums) {         vector c(105, 0);         for (int i = 0; i < nums.size(); i++) {             c[nums[i][0]] += 1;             c[nums[i][1] + 1] -= 1;         }         int ans = 0; int num = 0;         for (int i = 1; i < 105; i++) {             num += c[i];             ans += (num > 0);         }         return ans;     } }; 

就好像这个题目，我们可以小试牛刀直接进行树状数组

int a[60]; int lowbit(int x) { return x & (-x); } void add(int x, int p) {     for (int i = x; i <= 50; i += lowbit(i)) {         a[i] += p;     } } int query(int x) {     int sum = 0;     for (int i = x; i; i -= lowbit(i)) {         sum += a[i];     }return sum; }   class Solution { public:     bool isCovered(vector>& ranges, int left, int right) {         for (int i = 1; i <= 50; i++) a[i] = 0;         for (int i = 0; i < ranges.size(); i++) {             add(ranges[i][0], 1);             add(ranges[i][1] + 1, -1);         }         int flag = 1;         for (int i = left; i <= right; i++) {             int t = query(i);             if (!t) {                 flag = 0; break;             }         }return flag;     } };