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/**
* @Title: Solution167.java——
* @Package EasyCode
* @Description: TODO
* @author msdumin@gmail.com
* @date 2019年3月21日 下午9:48:31
* @version V1.0
*/
package EasyCode;
import java.lang.annotation.Target;
/**
* @ClassName: Solution167——TwoSum 有序数组 ：对撞指针
* @Description: TODO
* @author msdumin@gmail.com
* @date 2019年3月21日 下午9:48:31
*/
public class Solution167 {
/* //解法1：暴力解O(n2) 超时....
public int[] twoSum(int[] numbers, int target) {
int[] index = new int[2];
for(int i = 0 ; i < numbers.length ; i ++){
for(int j = i + 1 ; j < numbers.length ; j ++){
if(numbers[i] + numbers[j] == target){
index[0] = i+1;
index[1] = j+1;
}
}
}
return index;
}*/
/* //解法2：遍历一次+二分搜索法 时间复杂度为On(logn)
public static int[] twoSum(int[] numbers , int target){
int index[] = new int[2];
int n = numbers.length;
for(int i = 0 ; i < numbers.length ; i ++){
int ss = target - numbers[i];
if(binarySerch(numbers, i + 1, ss) != -1){
index[0] = i+1;
index[1] = binarySerch(numbers, i +1, ss) + 1;
break;
}
}
return index;
}
private static int binarySerch(int[] arr ,int l ,int target){
int r = arr.length - 1; //在[l,r]的范围内寻找target
while(l <= r){
int mid = l + (r-l)/2;
if(arr[mid] == target) return mid;
if(target > arr[mid])
l = mid + 1;
else {
r = mid - 1;
}
}
return -1;
}*/
//解法3：对撞指针 时间复杂度：O(n)
public static int[] twoSum(int[] numbers , int target){
int index[] = new int[2];
int p = 0;
int q = numbers.length - 1;
while(p < q){
if(target - numbers[p] == numbers[q]){
index[0] = p + 1;
index[1] = q + 1;
break;
}else if(target - numbers[p] > numbers[q])
p ++;
else
q--;
}
return index;
}
public static void main(String[] args) {
int[] arr = {1,2,3,4,4,9,45,65};
int target = 8;
int index[] = twoSum(arr,target);
System.out.println(index[0] + " " + index[1]);
}
}