题解 | #二分查找-II#

找左侧边界

class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 如果目标值存在返回下标，否则返回 -1
     * @param nums int整型vector 
     * @param target int整型 
     * @return int整型
     */
// 找左侧边界
    int search(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;

        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] == target) {
                right = mid - 1;
            }
        }

        if (left >= nums.size() || nums[left] != target) return -1;
        return left;
    }

找右侧边界

// 找右侧边界
    int search(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;

        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] == target) {
                left = mid + 1;
            }
        }

        if (right < 0 || nums[right] != target) return -1;
        return right;
    }
};

找左右边界

class Solution {
public:
    vector<int> searchRange(vector<int>& nums, int target) {
        int left = 0, right = nums.size() - 1;
        vector<int> res(2, -1);
        // 找左边界
        while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] == target) {
                right = mid - 1;
            }
        }

        if (left >= nums.size() || nums[left] != target)
            return res;
        else
            res[0] = left;

        // 找右边界
        left = 0, right = nums.size() - 1;
         while (left <= right) {
            int mid = left + (right - left) / 2;
            if (nums[mid] > target) {
                right = mid - 1;
            } else if (nums[mid] < target) {
                left = mid + 1;
            } else if (nums[mid] == target) {
                left = mid + 1;
            }
        }

        if (right < 0 || nums[right] != target)  return {-1, -1};

        res[1] = right;
        return res;

    }
};