java中经典算法及其代码整理

一、选择排序法

public static void selectSort(int[] a){
    int minIndex = 0;
    int temp = 0;
    if(a == null)||(a.length == 0){
        return;
    }
    for(i = 0; i < a.length-1; i++){
        minIndex = i;
        for(j = i+1; j < a.length; j++){
            if(a[j] < a[minIndex]){
                minIndex = j;
            }
        }
        if(minIndex != i){  //如果a[i]不是最小值，则将最小值放在a[i]位置
            temp = a[i];
            a[i] = a[minIndex];
            a[minIndex] = temp;
        }
    }
}

二、冒泡排序法

public static void BubbleSort(int[] a){
    int temp = 0;
    for(i = 0; i < a.length; i++){
        for(j = 1; j < a.length-i; j++){
            if(a[i] < a[j]){
                temp = a[i];
                a[i] = a[j];
                a[j] = temp;
            }
        }
    }
}

三、快速排序法

public class QuickSort{
    public void quickSort(int[] arr, low, high){
        if(low < high){
            int privotpos = partition(arr, low, high);
            quickSort(arr,low,privotpos-1);
            quickSort(arr,privotpos+1, high);
        }
    }

    public int partition(int[] arr, low, high){
        int privot = arr[low];
        while(low < high){
            while(low < high %& arr[low] <= privot) ++low;
            pritition = arr[low];
            while(low < high %& arr[high] >= privot) --high;
            privot = arr[high];
        }
        a[low]  = privot;
    }
}

四、二分查找法

public int binarySearch(int arr[], int key){
    int low = 0, high = arr.length, mid;
    while(low <= high){
        mid = (low + high) / 2;
        if(key == arr[mid]){
            return mid;
        }else if(key < arr[mid]){
            high = mid - 1; 
        }else{
            low = mid + 1;
        }
    }
    return -1;
}