Leetcode-34:Search for a Range

2018-01-31

问题描述：

SGiven an array of integers sorted in ascending order, find the starting and ending position of a given target value.

Your algorithm’s runtime complexity must be in the order of O(log n).

If the target is not found in the array, return [-1, -1].

问题示例

1
2
3

For example,
Given [5, 7, 7, 8, 8, 10] and target value 8,
return [3, 4].

我的答案

vector<int> searchRange(vector<int>& nums, int target) {
    vector<int> out;
    int start = -1;
    int end = -1;
    int high = nums.size() - 1;
    int low = 0;
    int mid;
    while (low<=high) {
        mid = (low + high)/2;
        if(nums[mid]<target){
            low = mid + 1;
        }else if(nums[mid]>target){
            high = mid - 1;
        }else{
            start = mid;
            end = mid;
            break;
        }
    }
    if(start != -1){
        while (start>=0) {
            if(nums[start] == target){
                start--;
            }else{
                break;
            }
        }
        start++;
    }
    if(end != -1){
        while (end<nums.size()) {
            if(nums[end] == target){
                end++;
            }else{
                break;
            }
        }
        end--;
    }
    out.push_back(start);
    out.push_back(end);
    return out;
}

其他高效答案

vector<int> searchRange(vector<int>& nums, int target) {
        int start = 0, end = nums.size() - 1;
        
        int mid = -1;
        while(start <= end) {
            mid = (start + end ) >> 1;
            if(nums[mid]  > target){
                end = mid - 1;
            }else if (nums[mid] < target){
                start = mid + 1;
            }else{
                break;
            }
        }
        if(mid < 0){
            return vector<int> {-1,-1};
        }
        if(nums[mid] == target){
            int i = mid, j = mid;
            while(i >= 0 && nums[i] == target) i--;
            while(j < nums.size() && nums[j] == target) j++;
            return vector<int>{i+1,j-1};
        }else{
            return vector<int> {-1,-1};
        }
    }