LeetCode(C++)-贪心算法（加油站、分发糖果、柠檬水找零、根据身高重建队列）

方法一：

class Solution {	//134. 加油站		//暴力解法 模拟一圈 
public:
	int canCompleteCircuit(vector& gas, vector& cost) {
		for (int i = 0; i < cost.size(); i++) {
			int rest = gas[i] - cost[i];
			int index = (i + 1) % cost.size();
			while (rest > 0 && index != i) {
				rest += gas[index] - cost[index];
				index = (index + 1) % cost.size();
			}
			if (rest >= 0 && index == i)return i;
		}
		return -1;
	}
};

方法二：

class Solution {	//134. 加油站  贪心算法 找局部最优，当前累加rest[j]的和curSum一旦小于0，起始位置至少要是j+1，因为从j开始一定不行 确定全局最优
public:
	int canCompleteCircuit(vector& gas, vector& cost) {
		int start = 0;
		int curSum = 0;
		int totalSum = 0;
		for (int i = 0; i < gas.size(); i++) {
			curSum += gas[i] - cost[i];
			totalSum += gas[i] - cost[i];
			if (curSum < 0) {
				start = i + 1;
				curSum = 0;
			}
		}
		if (totalSum < 0)return -1;
		return start;
	}

int main() {
	vector gas = { 1, 2, 3, 4, 5 };
	vector cost = { 3, 4, 5, 1, 2 };
	Solution s;
	int result = s.canCompleteCircuit(gas, cost);
	cout << result << endl;
	return 0;
}

class Solution {	//135. 分发糖果 先从前向后遍历，比较右边孩子评分比左边孩子评分高的情况 再从后向前遍历，比较左边孩子评分比右边孩子评分高的情况
public:
	int candy(vector& ratings) {
		vector nums(ratings.size(), 1);
		//从前向后
		for (int i = 1; i < ratings.size(); ++i) {
			if (ratings[i] > ratings[i - 1]) {
				nums[i] = nums[i - 1] + 1;
			}
		}
		//从后向前
		for (int i = ratings.size() - 2; i >= 0; --i) {
			if (ratings[i] > ratings[i + 1]) {
				nums[i] = max(nums[i], nums[i + 1] + 1);
			}
		}
		int result = 0;
		for (int i = 0; i < nums.size(); ++i) {
			result += nums[i];
		}
		return result;
	}
};

class Solution {	//860. 柠檬水找零 分情况 遇见5直接bill5++；遇见10,bill10++,bill5--；遇见20如果bill10>0，bill10--,bill5--，否则bill5-=3；最后判断bill5和bill10是否小于0，小于0就说明找不开，返回false
public:
	bool lemonadeChange(vector& bills) {
		int bill5 = 0;
		int bill10 = 0;
		for (int i = 0; i < bills.size(); ++i) {
			if (bills[i] == 5)bill5++;
			if (bills[i] == 10){
				bill10++;
				bill5--;
			}
			if (bills[i] == 20) {
				if (bill10 > 0) {
					bill10--;
					bill5--;
				}
				else bill5 -= 3;
			}
			if (bill5 < 0 || bill10 < 0)return false;
		}
		return true;
	}
};

class Solution {	//406. 根据身高重建队列 先按身高排序（从大到小），身高相同的按k从小到大排序，然后从身高高的开始，将k作为下标 重新插入
public:
	class mySort{
	public:
		bool operator()(vector const& first, vector const& second) {
			if (first[0] == second[0]) return first[1] < second[1];
			return first[0] > second[0];
		}
	};

	vector> reconstructQueue(vector>& people) {
		sort(people.begin(), people.end(), mySort());
		vector> result;
		vector>::iterator it;
		for (int i = 0; i < people.size(); ++i) {
			it = result.begin() + people[i][1];
			result.insert(it, people[i]);
		}
		return result;
	}
};

int main() {
	vector> people = { { 7, 1 }, { 4, 4 }, { 7, 0 }, { 5, 0 }, { 6, 1 }, { 5, 2 } };
	Solution s;
	vector> result = s.reconstructQueue(people);
	return 0;
}

代码随想录