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ThreeSumClosest.java
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145 lines (121 loc) · 4.73 KB
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import java.util.Arrays;
/**
* 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. You may assume that each input would have exactly one solution.
* 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).
* <p/>
* The solution is to use two nested loops to enumerate the combination of num[i], num[j],
* and then use binary search to locate the numbers which may have the closest distance with the target.
* The complexity of this algorithm is O(n^2*logn).
*/
public class ThreeSumClosest {
public static void main(String[] args) {
int[] a = new int[]{-1, 2, 1, -4};
int target = 1;
int[] result = threeSumClosest(a, target);
System.out.println(Arrays.toString(result));
int[] result1 = threeSumClosest1(a, target);
System.out.println(Arrays.toString(result1));
}
public static int[] threeSumClosest(int[] a, int target) {
int[] result = new int[3];
if (a.length < 3)
return result;
Arrays.sort(a);
int min_distance = Integer.MAX_VALUE;
for (int i = 0; i < a.length - 2; i++) { // extra two element needed, so i<a.length-2
for (int j = i + 1; j < a.length - 1; j++) { // extra one element needed, so j<a.length-1
int val = target - a[i] - a[j];
int begin = j + 1, end = a.length - 1, mid, sum;
int[] temp = new int[3];
while (begin <= end) {
mid = (begin + end) / 2;
if (a[mid] == val) {
result[0] = a[i];
result[1] = a[j];
result[2] = a[mid];
return result;
} else if (a[mid] < val) {
begin = mid + 1;
} else {
end = mid - 1;
}
}
if (begin > a.length - 1) {
sum = a[i] + a[j] + a[end];
temp[0] = a[i];
temp[1] = a[j];
temp[2] = a[end];
} else if (end < j + 1) {
sum = a[i] + a[j] + a[begin];
temp[0] = a[i];
temp[1] = a[j];
temp[2] = a[begin];
} else {
int d1 = a[i] + a[j] + a[begin];
int d2 = a[i] + a[j] + a[end];
int d1_distance = Math.abs(d1 - target);
int d2_distance = Math.abs(d2 - target);
if (d1_distance < d2_distance) {
sum = d1;
temp[0] = a[i];
temp[1] = a[j];
temp[2] = a[begin];
} else {
sum = d2;
temp[0] = a[i];
temp[1] = a[j];
temp[2] = a[end];
}
}
if (Math.abs(sum - target) < min_distance) {
min_distance = Math.abs(sum - target);
result = temp.clone();
}
}
}
return result;
}
// non binary search O(n^3)
public static int[] threeSumClosest1(int[] a, int target) {
int[] result = new int[3];
if (a.length < 3)
return result;
Arrays.sort(a);
int min_distance = Integer.MAX_VALUE;
int x, y, z, sum, temp_distance;
for (int i = 0; i < a.length - 2; i++) {
x = a[i];
for (int j = i + 1, k = a.length - 1; j < k; ) {
y = a[j];
z = a[k];
sum = x + y + z;
temp_distance = Math.abs(sum - target);
if (sum < target) {
if (temp_distance < min_distance) {
min_distance = temp_distance;
result[0] = x;
result[1] = y;
result[2] = z;
}
j++;
} else if (sum > target) {
if (temp_distance < min_distance) {
min_distance = temp_distance;
result[0] = x;
result[1] = y;
result[2] = z;
}
k--;
} else {
result[0] = x;
result[1] = y;
result[2] = z;
return result;
}
}
}
return result;
}
}