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  • Chap5: question: 29

    29. 数组中出现次数超过一半的数字.

    方法a. 排序取中       O(nlogn).

    方法b. partition 函数分割找中位数     >=O(n).

    方法c. 设计数变量,扫描一遍。     O(n).

    #include <stdio.h>
    int getNumber(int data[], int length){
    /*  if(checkInvalidArray(data, length)) return 0;  */
        int count = 1, value = data[0];
        for(int i = 1; i < length; ++i)
        {
            if(count == 0){
                value = data[i];
            }else if(data[i] == value){
                ++count;
            }else
                --count;
        }
        return value;
    }
    int main(){
        int numbers[] = {2, 2, 2, 2, 6, 6, 6, 6, 6};
        int value = getNumber(numbers, sizeof(numbers) / 4);
    /*  if(value != 0 || !checkInvalidArray(data, length))  */
        printf("%d
    ", value);
        return 0;
    }
    

    shot

    30. 最小的 k 个数

    a. partition 函数找到第 k 个数.   >=O(n)

    #include <stdio.h>
    int partition(int data[], int low, int high){
        int value = data[low];
        while(low < high){
            while(low < high && data[high] >= value) --high;
            data[low] = data[high];
            while(low < high && data[low] <= value) ++low;
            data[high] = data[low];
        }
        data[low] = value;
        return low;
    }
    void getKNumber(int input[], int length, int out[], int k){
        if(!input || !out || length < 1 || k > length || k < 1) return;
        int low = 0, high = length - 1, index;
        do{
            index = partition(input, low, high);
            if(index < k-1) low = index + 1;
            else if(index > k-1) high = index - 1;
        }while(index != k-1);
        for(int i = 0; i < k; ++i)
            out[i] = input[i];
    }
    int main(){
        int numbers[10] = {3, 5, 2, 6, 7, 4, 9, 1, 2, 6};
        int k = 5;
        getKNumber(numbers, 10, numbers, k);
        for(int i = 0; i < k; ++i)
            printf("%-3d", numbers[i]);
        printf("
    ");
        return 0;
    }
    

    shot

    b. 构造k 个元素的大顶堆

    #include <stdio.h>
    void HeapAdjust(int data[], int endIndex, int father){
        if(!data || endIndex < 0 || father > endIndex || father < 0) return;
        int value = data[father]; // set data[0] to save the value of original father
        for(int child = 2*father+1; child <= endIndex; child = 2*father+1){
            if(child < endIndex && data[child] < data[child+1]) ++child;
            if(data[child] < value) break;
            else data[father] = data[child];
            father = child;
        }
        data[father] = value;
    }
    void getKNumber(int input[], int length, int out[], int k){
        if(!input || !out || length < 1 || k > length || k < 1) return;
        for(int i = 0; i < k; ++i)
            out[i] = input[i];
        for(int i = k/2-1; i >= 0; --i)
            HeapAdjust(out, k-1, i);
        for(int i = k; i < length; ++i){
            if(input[i] < out[0]){
                out[0] = input[i];
                HeapAdjust(out, k-1, 0);
            }
        }
    }
    int main(){
        int numbers[10] = {3, 5, 2, 6, 7, 4, 9, 1, 2, 6};
        enum{ k = 1};
        int out[k+1] = {0};
        getKNumber(numbers, 10, out, k);
        for(int i = k-1; i >= 0; --i){
            int tem = out[i];
            out[i] = out[0];
            out[0] = tem;
            printf("%-3d", out[i]);
            HeapAdjust(out, i-1, 0); // DESC
        }
        printf("
    ");
        return 0;
    }
    

    shot

    31. 连续子数组的最大和

    #include <stdio.h>
    bool Invalid_Input = false;
    int getKNumber(int data[], int length){
        Invalid_Input = false;
        if(data == NULL || length < 1) {
            Invalid_Input = true;
            return 0;
        }
        int maxSum = 0x80000000;
        int curSum = 0;
        for(int i = 0; i < length; ++i){
            if(curSum < 0) curSum = data[i];
            else curSum += data[i];
            if(curSum > maxSum) maxSum = curSum;
        }
        return maxSum;
    }
    int main(){
        int numbers[] = {1,-2, 3, 10, -4, 7, 2, -5, -2, 4, -5, 4};
        int maxSum = getKNumber(numbers, sizeof(numbers)/4);
        if(!Invalid_Input)
            printf("%d
    ", maxSum);
        return 0;
    }
    

    shot

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  • 原文地址:https://www.cnblogs.com/liyangguang1988/p/3703688.html
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