leetcode/3SumWithMultiplicity.java at master · mengli/leetcode · GitHub

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/**
 * Given an integer array A, and an integer target, return the number of tuples i, j, k such that i < j < k and A[i] + A[j] + A[k] == target.
 *
 * As the answer can be very large, return it modulo 10^9 + 7.
 */
classSolution {
publicintthreeSumMulti(int[] A, inttarget) {
Map<Integer, Integer> count = newHashMap<>();
for (inta : A) {
if (count.containsKey(a)) {
count.put(a, count.get(a) + 1);
 } else {
count.put(a, 1);
 }
 }
Object[] elements = count.keySet().toArray();
Integer[] integers = Arrays.copyOf(elements, elements.length, Integer[].class);
longret = 0;
Arrays.sort(integers);
for (inti = 0; i < integers.length; i++) {
for (intj = i; j < integers.length; j++) {
intrest = target - integers[i] - integers[j];
if (count.containsKey(rest) && rest >= integers[j]) {
if (integers[i] == integers[j] && integers[j] == rest) {
ret += calculate(count.get(rest), 3);
 } elseif (integers[i] == rest && integers[i] != integers[j]) {
ret += (calculate(count.get(integers[i]), 2) * count.get(integers[j]));
 } elseif (integers[j] == rest && integers[i] != integers[j]) {
ret += (calculate(count.get(integers[j]), 2) * count.get(integers[i]));
 } elseif (integers[i] == integers[j] && integers[i] != rest) {
ret += (calculate(count.get(integers[j]), 2) * count.get(rest));
 } else {
ret += (count.get(integers[i]) * count.get(integers[j]) * count.get(rest));
 }
 }
 }
 }
return (int) (ret % (1e9 + 7));
 }

privatelongcalculate(longx, longn) {
if (n == 2) {
returnx * (x - 1) / 2;
 }
returnx * (x - 1) * (x - 2) / 6;
 }
}