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927.cpp
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927.cpp
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class Solution {
public:
vector<int> threeEqualParts(vector<int>& arr) {
int oneCnt = 0;
int n = arr.size();
for (auto& bit : arr) {
if (bit & 1) oneCnt++;
}
if (oneCnt == 0) return {0, n - 1};
if (oneCnt % 3 != 0) return {-1, -1};
int target = oneCnt / 3;
int firstIdx = -1; // first 1 [1, k]
int secondIdx = -1; // k + 1 [k + 1, 2k]
int thirdIdx = -1; // 2k + 1 [2K + 1, 3k]
oneCnt = 0;
for (int i = 0; i < n; ++i) {
if (arr[i] & 1) oneCnt++;
if (oneCnt == 1 && firstIdx == -1) firstIdx = i;
else if (oneCnt == target + 1 && secondIdx == -1) secondIdx = i;
else if (oneCnt == 2 * target + 1) {
thirdIdx = i;
break;
}
}
// check each partition
while (thirdIdx < n) {
if (arr[firstIdx] == arr[secondIdx] && arr[secondIdx] == arr[thirdIdx]) {
firstIdx++;
secondIdx++;
thirdIdx++;
}
else break;
}
if (thirdIdx != n) return {-1, -1};
return {firstIdx - 1, secondIdx};
}
};