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3 Sum Closest.java
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57 lines (48 loc) · 1.88 KB
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M
3Sum 的一种简单形式, 并且都没有找index, value, 而只是找个sum罢了.
double for loop。 2Sum只能用土办法 left/right 2 pointers。 O(n^2)
注意：check closest时候用long, 以免int不够用
```
/*
Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers.
Note
You may assume that each input would have exactly one solution.
Example
For example, given array S = {-1 2 1 -4}, and target = 1. The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).
Tags Expand
Two Pointers Sort Array
*/
/*
Thoughts:
Similar to 3 SUM.
Starting from the left-element, assume it's the solution. Move the 2 pointers in the right-side-array.
Using the two pointers, trying to find ele1 + ele2 + ele3 = closest number to target.
Note: for comparing closet, use initial value Integer.MAX_VALUE. Be aware of the overflow of integer, use long to handle.
*/
public class Solution {
public int threeSumClosest(int[] num, int target) {
if (num == null || num.length < 3) {
return Integer.MAX_VALUE;
}
Arrays.sort(num);
long closest = (long) Integer.MAX_VALUE;
for (int i = 0; i < num.length - 2; i++) {
int left = i + 1;
int right = num.length - 1;
while (left < right) {
int sum = num[i] + num[left] + num[right];
if (sum == target) {
return sum;
} else if (sum < target) {
left++;
} else {
right--;
}
closest = Math.abs(sum - target) < Math.abs(closest - target)
? (long) sum : closest;
}//while
}//for
return (int) closest;
}
}
```