合并区间

class Solution {
public:static bool cmp(const vector<int> & a,const vector<int> & b){return a[0]<b[0];}vector<vector<int>> merge(vector<vector<int>>& intervals) {sort(intervals.begin(),intervals.end(),cmp);vector<int> tmp=intervals[0];vector<vector<int>> res;int n=intervals.size();for(int i=1;i<n;i++){if(tmp[1]>=intervals[i][0]){tmp[1]=tmp[1]>intervals[i][1]?tmp[1]:intervals[i][1];}else{res.push_back(tmp);tmp=intervals[i];}}res.push_back(tmp);return res;}
};

和分割字符串那个一样

单调递增的数字

class Solution {
public:int monotoneIncreasingDigits(int k) {string s=to_string(k);int index=-1;int n=s.size();for(int i=0;i<n-1;i++){if(s[i]>s[i+1]){s[i]--;index=i+1;while(index>1&&s[index-1]<s[index-2]){index--;s[index-1]--;}break;}}for(int i=index;i>=0&&i<n;i++){s[i]='9';}int res=stoi(s);return res;}
};

监控二叉树

class Solution {
public:int minCameraCover(TreeNode* root) {unordered_map<TreeNode* ,int> mymap;stack<TreeNode*> sta;sta.push(root);TreeNode* cur=root;int count=0;while(!sta.empty()){cur=sta.top();sta.pop();if(cur){sta.push(cur);sta.push(nullptr);if(cur->left){sta.push(cur->left);}if(cur->right){sta.push(cur->right);}}else{cur=sta.top();sta.pop();bool put=0;if(cur->right){if(mymap[cur->right]==0){put=1;}else if(mymap[cur->right]==2){mymap[cur]=1;}}if(cur->left){if(mymap[cur->left]==0){put=1;}else if(mymap[cur->left]==2){mymap[cur]=1;}}if(put){mymap[cur]=2;count++;mymap[cur->left]=mymap[cur->right]=1;}else if(cur==root&&!mymap[cur]){mymap[cur]=2;count++;}}}    return count;}
};