剑指offer 38题

最新推荐文章于 2021-06-23 12:15:28 发布
victeer
最新推荐文章于 2021-06-23 12:15:28 发布
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分类专栏：刷题
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题目：
统计一个数字在排序数组中出现的次数。如， 输入排序数组{1, 2, 3, 3, 3, 3, 3, 4, 5} 和数字3，由于3在数组中出现4次，因此输出4.
在牛客网上做的测试。
第一版(正确)：
    int GetNumberOfK(vector<int> data ,int k) {
        int i = 0;
        for (auto x: data) {
            if (x == k) {
                i++;
            }
        }
        return i;
    }
第二版(错误) :
class Solution {
public:
    int GetNumberOfK(vector<int> data, int k) {
        int first = GetFirstK(data, k, 0, data.size() - 1);
        if (first == -1) return 0;
        int last = GetLastK(data, k, first, data.size() - 1);
        if (last == -1) return 0;
         
        return (last - first + 1);
    }
     
    int GetFirstK(const vector<int>& data, int k, int begin, int end) {
        cout << "Get Fist K:  begin:" << begin << " end:" << end << endl;
        if (begin > end) {
            return -1;
        }else if(begin == end) {
            return begin;
        }
         
        int mid = (begin + end) / 2;
        if (data[mid] > k) {
            return GetFirstK(data, k, begin, mid - 1);
        } else if (data[mid] == k) {
            return GetFirstK(data, k, begin, mid);
        } else {
            return GetFirstK(data, k, mid + 1, end);
        }
    }
     
    int GetLastK(const vector<int>& data, int k, int begin, int end) {
        cout << "Get Last K:  begin:" << begin << " end:" << end << endl;
        if (begin > end) {
            return -1;
        } else if(begin == end) {            return begin;
      }
         
        int mid = (begin + end) / 2;
        if (data[mid] > k) {
            return GetLastK(data, k, begin, mid - 1);
        } else if (data[mid] == k) {
            return GetLastK(data, k, mid, end);
        } else {
            return GetLastK(data, k, mid + 1, end);
        }
    }
第三版(正确):
class Solution {
public:
    int GetNumberOfK(vector<int> data, int k) {
        if (data.size() == 0) {
            return 0;
        }
        int first = GetFirstK(data, k, 0, data.size() - 1);
        if (first == -1) return 0;
        int last = GetLastK(data, k, first, data.size() - 1);
         
        return (last - first + 1);
    }
     
    int GetFirstK(const vector<int>& data, int k, int begin, int end) {
        if (begin > end) {
            return -1;
        }
         
        int mid = (begin + end) / 2;
        int value = data[mid];
        if (value > k) {
            end = mid - 1;
        } else if (value == k) {
            if(begin == mid || data[mid - 1] != k)
            {  
                return mid;
            } else {
                end = mid - 1;
            }
        } else {
            begin = mid + 1;
        }
        return GetFirstK(data, k, begin, end);
    }
     
    int GetLastK(const vector<int>& data, int k, int begin, int end) {
        if (begin > end) {
            return -1;
        }
         
        int mid = (begin + end) / 2;
        int value = data[mid];
        if (value > k) {
            end = mid - 1;
        } else if (value == k) {
            if(mid == end || data[mid + 1] != k)
            {  
                return mid;
            } else {
                begin = mid + 1;
            }
        } else {
            begin = mid + 1;
        }
        return GetLastK(data, k, begin, end);
    }
};