acwing-week-1-二分-Leetcode-34，35， 69， 74， 240，153，278， 162，287，275

目錄

 

Leetcode-34

Leetcode-35

Leetcode-69

Leetcode-74

Leetcode-240

Leetcode-153

Leetcode-278

Leetcode-162

Leetcode-287

Leetcode-275

---

以上十道Leetcode題目都可使用二分的思想來解決

在解題的過程中都使用了二分模板

在解決的過程中關鍵是要從題目中找到將總體分爲兩個部分的性質，從而使用二分法解決問題。

Leetcode-34

class Solution{
public:
	vector<int> searchRange(vector<int>& nums, int target){
		if (nums.empty()){
			return {-1, -1};
		}
		int l = 0, r = nums.size() - 1;
		while(l < r){
			int mid = l + r >> 1;
			if(nums[mid] >=target) r = mid;
			else l = mid + 1;
		}
		
		if(nums[r] != target) return {-1, -1};
		int start = r;

		l = 0, r = nums.size() - 1;
		while(l < r){
			int mid = l + r + 1 >> 1;
			if(nums[mid] <= target) l = mid;
			else r = mid - 1;
		}
		int end = r;
		return {start, end};
	}
};

// class Solution{
// public:
// 	std::vector<int> searchRange(std::vector<int> &nums, int target){
// 		std::vector<int> result;
// 		int left = left_bound(nums, target);
// 		result.push_back(left);
// 		int right = right_bound(nums, target);
// 		result.push_back(right);
// 		return result;
// 	}
// private:
// 	int left_bound(std::vector<int> &nums, int target){
// 		int begin = 0;
// 		int end = nums.size()-1;
// 		while(begin <= end){
// 			int mid = (begin+end)/2;
// 			if(target == nums[mid]){
// 				if(mid == 0 || nums[mid-1] < target){
// 					return mid;
// 				}
// 				end = mid - 1;
// 			}
// 			else if(target < nums[mid]){
// 				end = mid - 1;
// 			}
// 			else if(target > nums[mid]){
// 				begin = mid + 1;
// 			}
// 		}
// 		return -1;
// 	}
	
// 	int right_bound(std::vector<int> &nums, int target){
// 		int begin = 0;
// 		int end = nums.size() - 1;
// 		while(begin <= end){
// 			int mid = (begin + end) / 2;
// 			if(target == nums[mid]){
// 				if(mid == nums.size() - 1 || nums[mid + 1] >target){
// 					return mid;
// 				}
// 				begin = mid + 1;
// 			}
// 			else if(target < nums[mid]){
// 				end = mid - 1;
// 			}
// 			else if(target > nums[mid]){
// 				begin = mid + 1;
// 			}
// 		}
// 		return -1;
// 	}
// };

Leetcode-35

class Solution{
public:
	int searchInsert(vector<int>& nums, int target){
		if (nums.empty() || nums.back() < target){
			return nums.size();
		}
		int l = 0, r = nums.size() - 1;
		while(l < r){
			int mid = l + r >> 1;
			if (nums[mid] >= target){
				r = mid;
			}
			else{
				l = mid + 1;
			}	
		}
		return r;
	}
};

// class Solution{
// public:
// 	int searchInsert(std::vector<int> &nums, int target){
// 		int index = -1;
// 		int begin = 0;
// 		int end = nums.size() - 1;
// 		while(index == -1){
// 			int mid = (begin+end)/2;
// 			if(target == nums[mid]){
// 				index = mid;
// 			}
// 			else if(target < nums[mid]){
// 				if(mid == 0 || target > nums[mid-1]){
// 					index = mid;
// 				}
// 				end = mid - 1;
// 			}
// 			else if(target > nums[mid]){
// 				if(mid == nums.size()-1 || target < nums[mid+1]){
// 					index = mid + 1;
// 				}
// 				begin = mid + 1;
// 			}
// 		}
// 		return index;
// 	}
// };

Leetcode-69

class Solution{
public:
	int mySqrt(int x){
		int l = 0, r = x;
		while(l < r){
			int mid = l + (long long)r + 1 >> 1;
			if (mid <= x / mid) l = mid;
			else r = mid - 1;
		}
		return r;
	}
};

Leetcode-74

class Solution {
public:
    bool searchMatrix(vector<vector<int>>& matrix, int target) {
        if (matrix.empty() || matrix[0].empty()) return false;

        int n = matrix.size(), m = matrix[0].size();
        int l = 0, r = n * m - 1;
        while(l < r){
        	int mid = l + r >> 1;
        	if(matrix[mid / m][mid % m] >= target) r = mid;
        	else l = mid + 1;
		}
		if(matrix[r / m][r % m] != target) return false;
  		return true;	
    }
};

Leetcode-240

class Solution:
    def searchMatrix(self, matrix, target):
        if not matrix:
            return False
        i = 0
        j = len(matrix[0]) - 1
        while i < len(matrix) and j >= 0:
            value = matrix[i][j]
            if value == target:
                return True
            elif value > target:
                j -= 1
            else:
                i += 1
        return False

Leetcode-153

class Solution {
public:
    int findMin(vector<int>& nums) {
        int l = 0, r = nums.size() - 1;
        while (l < r){
        	int mid = l + r >> 1;
        	if (nums[mid] <= nums.back()) r = mid;
        	else l = mid + 1;
        }
        return nums[r];
    }
};

Leetcode-278

// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n) {
        int l = 1, r = n;
        while (l < r){
        	int mid = (long long)l + r >> 1;
        	if (isBadVersion(mid)) r = mid;
        	else l = mid + 1;
        }
        return r;
    }
};

Leetcode-162

class Solution {
public:
    int findPeakElement(vector<int>& nums) {
        int l = 0, r = nums.size() - 1;
        while (l < r){
        	int mid = l + r >> 1;
        	if (nums[mid] > nums[mid + 1]) r = mid;
        	else l = mid + 1;
        }
        return r;
    }
};

Leetcode-287

class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        int n = nums.size() - 1;
        int l = 1, r = n;
        while (l < r){
        	int mid = l + r >> 1;
        	int cnt = 0;
        	for (auto x : nums)
        		if (x >= l && x <= mid)
        			cnt++;
        	if (cnt > mid - l + 1) r = mid;
        	else l = mid + 1;
        }
        return r;
    }
};

Leetcode-275

class Solution {
public:
    int hIndex(vector<int>& citations) {
         int l = 0, r = citations.size();
         while(l < r){
         	int mid = l + r + 1 >> 1;
         	if(citations[citations.size() - mid] >= mid) l = mid;
         	else r = mid - 1;
         }
         return r;
    }
};