常用算法积累

static int add(int n)
{
    int sum = 0;
    n && (sum = add(n - 1) + n);
    return sum;
}

static void sort_q(int *a, int low, int high)
{
    if (low >= high) {
        return;
    }
    int value = a[low];
    int leftIdx = low;
    int rightIdx = high;
    while (leftIdx < rightIdx) {
        while (leftIdx < rightIdx && value <= a[rightIdx]) {
            rightIdx--;
        }
        a[leftIdx] = a[rightIdx];
        
        while (leftIdx < rightIdx && value >= a[leftIdx]) {
            leftIdx++;
        }
        a[rightIdx] = a[leftIdx];
    }
    
    a[leftIdx] = value;
    sort_q(a, low, leftIdx - 1);
    sort_q(a, leftIdx + 1, high);
}

static int search_half(int *a, int len, int key)
{
    int rst = -1;
    int low = 0;
    int high = len - 1;
    int middle;
    while (low <= high) {
        middle = (high + low) / 2;
        if (key == a[middle]) {
            return middle;
        } else if (key > a[middle]) {
            low = middle + 1;
        } else if (key < a[middle]) {
            high = middle - 1;
        }
    }
    return rst;
}