Java常用的排序查找算法
public static void main(String[] args) {
// bubbleSort();
// int[] a = {20,2,10,8,12,17,4,25,11,6,33,13,24};
// int start = 0;
// int end = a.length-1;
// sort(a,start,end);
// for(int i = 0; i<a.length; i++){
// System.out.print(a[i]+",");
// }
// choseSort();
// nsertSort();
// sequential();
binarySearch();
}
/**冒泡排序*/
public static void bubbleSort(){
int[] score = {20,2,10,8,12,17,4,25,11,6,33,13,24};
//冒泡排序
for (int i = 0; i < score.length -1; i++){ //最多做n-1趟排序
for(int j = 0 ;j < score.length - i - 1; j++){
//对当前无序区间score[0......length-i-1]进行排序
//(j的范围很关键,这个范围是在逐步缩小的)
if(score[j] > score[j + 1]){ //把小的值交换到后面
int temp = score[j];
score[j] = score[j + 1];
score[j + 1] = temp;
}
}
}
System.out.print("最终排序结果:");
for(int a = 0; a < score.length; a++){
System.out.print(score[a] + ",");
}
}
/**快速排序*/
public static void sort(int[] a,int low,int high){
int start = low;
int end = high;
int key = a[low];
while(end>start){
//从后往前比较
while(end>start&&a[end]>=key) //如果没有比关键值小的,比较下一个,直到有比关键值小的交换位置,然后又从前往后比较
end--;
if(a[end]<=key){
int temp = a[end];
a[end] = a[start];
a[start] = temp;
}
//从前往后比较
while(end>start&&a[start]<=key)//如果没有比关键值大的,比较下一个,直到有比关键值大的交换位置
start++;
if(a[start]>=key){
int temp = a[start];
a[start] = a[end];
a[end] = temp;
}
//此时第一次循环比较结束,关键值的位置已经确定了。左边的值都比关键值小,右边的值都比关键值大,但是两边的顺序还有可能是不一样的,进行下面的递归调用
}
//递归
if(start>low) sort(a,low,start-1);//左边序列。第一个索引位置到关键值索引-1
if(end<high) sort(a,end+1,high);//右边序列。从关键值索引+1到最后一个
}
/**选择排序*/
public static void choseSort(){
int[] toBeSorted = {20,2,10,8,12,17,4,25,11,6,33,13,24};
for(int i = 0; i < toBeSorted.length; i++){
for(int j = i+1; j < toBeSorted.length; j++){
if(toBeSorted[i] > toBeSorted[j]){
int temp = toBeSorted[i];
toBeSorted[i] = toBeSorted[j];
toBeSorted[j] = temp;
}
}
}
for(int i = 0; i <toBeSorted.length; i++){
System.out.print(toBeSorted[i]+",");
}
}
/**插入排序*/
public static void nsertSort(){
int[] arr = {20,2,10,8,12,17,4,25,11,6,33,13,24};
int i, j;
int n = arr.length;
int target;
//假定第一个元素被放到了正确的位置上
//这样,仅需遍历1 - n-1
for (i = 1; i < n; i++){
j = i;
target = arr[i];
while (j > 0 && target < arr[j - 1]){
arr[j] = arr[j - 1];
j--;
}
arr[j] = target;
}
for(int a = 0; a < arr.length; a++){
System.out.print(arr[a] + ",");
}
}
/**顺序查找*/
public static void sequential(){
int[] arr = {20,2,10,8,12,17,4,25,11,6,33,13,24};
int key = 6;
for(int i=0;i<arr.length;i++){
if(key == arr[i]){
System.out.print("第"+(i+1)+"个");
}
}
}
/**折半查找*/
public static void binarySearch(){
int[] arr = {20,2,10,8,12,17,4,25,11,6,33,13,24};
int low = 0;
int high = arr.length - 1;
int key = 6;
while ((low <= high) && (low <= arr.length - 1)
&& (high <= arr.length - 1)) {
int middle = (high + low) >> 1;
if (key == arr[middle]) {
System.out.print("第"+(middle+1)+"个");
break;
} else if (key < arr[middle]) {
high = middle - 1;
} else {
low = middle + 1;
}
}
}