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ThreeSum.java
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ThreeSum.java
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import java.util.Arrays;
import java.util.List;
import java.util.ArrayList;
public class ThreeSum {
public static void main(String[] args) {
int[] nums = new int[]{-1, 0, 1, 2, -1, -4};
System.out.println(threeSum(nums));
}
public static List<List<Integer>> threeSum(int[] nums) {
/** 思路: 先把元素都排序,扫描一次,每次在剩下的元素中利用已排序的2Sum方法,
* 寻找剩下的元素中是否有两个元素的和等于0 - nums[i]。
**/
Arrays.sort(nums);
List<List<Integer>> result = new ArrayList<>();
for (int i = 0; i < nums.length - 2; i++) {
if (i > 0 && nums[i] == nums[i-1]) continue; //如果下一个元素与前一个元素相同,跳过重复
int low = i + 1;
int high = nums.length - 1;
int complement = 0 - nums[i];
int pairSum = 0;
while (low < high) {
pairSum = nums[low] + nums[high];
if (pairSum < complement) low++;
if (pairSum > complement) high--;
if (pairSum == complement) {
result.add(Arrays.asList(nums[i], nums[low++], nums[high--]));
while(low < high && nums[low] == nums[low - 1]) low++; //如果下一个元素与前一个元素相同,跳过重复
while(high > low && nums[high] == nums[high + 1]) high--; //如果下一个元素与后一个元素相同,跳过重复,千万注意这边是递减!
}
}
}
return result;
}
}