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// 3445. Maximum Difference Between Even and Odd Frequency II
#include "leetcode.h"
/*
* you are given a string 's' and an integer 'k'. your task is to find the
* maximum difference between the frequency of two characters 'freq[a], -
* freq[b]', in a substring 'subs' of 's' such that 'subs' has a size of at
* least 'k', character 'a' has an odd frequency in 'subs', character 'b' has an
* even frequency in 'subs'. return the maximum difference. note that 'subs' can
* contain more than 2 distinct characters.
*/
static int upper_bound(const int *arr, int n, int key) {
int low = 0, high = n;
while (low < high) {
int mid = low + ((high - low) >> 1);
if (arr[mid] <= key)
low = mid + 1;
else
high = mid;
}
return low;
}
int maxDifference(char *s, int k) {
int n = strlen(s);
if (!n || k > n)
return -1;
int (*freq)[5] = malloc(sizeof(int[5]) * n), present[5] = {0};
if (!freq)
return -1;
for (int i = 0; i < n; i++) {
int c = s[i] - '0';
if (!i)
memset(freq[i], 0, sizeof(int) * 5);
else
memcpy(freq[i], freq[i - 1], sizeof(int) * 5);
freq[i][c]++;
present[c] = 1;
}
int ans = INT_MIN;
for (int a = 0; a < 5; a++) {
if (!present[a])
continue;
for (int b = 0; b < 5; b++) {
if (!present[b] || a == b)
continue;
int *idx_list[4], *val_list[4], size[4];
for (int i = 0; i < 4; i++) {
idx_list[i] = (int *)malloc(sizeof(int) * n);
val_list[i] = (int *)malloc(sizeof(int) * n);
size[i] = 0;
}
int odd = 0, even = 0;
for (int i = 0; i < n; i++) {
int c = s[i] - '0';
if (c == a)
odd++;
else if (c == b)
even++;
if ((odd & 1) && (even & 1) == 0 && (i + 1) >= k && even > 0) {
int diff = odd - even;
if (diff > ans)
ans = diff;
}
int key1 = ((odd % 2 == 0) ? 1 : 0) << 1 | ((even % 2 == 0) ? 0 : 1);
if (size[key1] > 0) {
int limit = i - k;
if (limit >= 0) {
int pos = upper_bound(idx_list[key1], size[key1], limit);
if (pos > 0) {
int prev = pos - 1, l = 0, r = prev, curr_min = INT_MAX;
while (l <= r) {
int mid = (l + r) >> 1, j = idx_list[key1][mid];
if (freq[i][b] != freq[j][b]) {
int v = val_list[key1][mid];
if (v < curr_min)
curr_min = v;
l = mid + 1;
} else
r = mid - 1;
}
if (curr_min != INT_MAX) {
int cur = odd - even - curr_min;
if (cur > ans)
ans = cur;
}
}
}
}
int key2 = (odd % 2) << 1 | (even % 2), curr_diff = odd - even;
if (!size[key2]) {
idx_list[key2][0] = i;
val_list[key2][0] = curr_diff;
size[key2] = 1;
} else {
int prev_min = val_list[key2][size[key2] - 1];
int new_min = (prev_min < curr_diff) ? prev_min : curr_diff;
idx_list[key2][size[key2]] = i;
val_list[key2][size[key2]] = new_min;
size[key2]++;
}
}
for (int i = 0; i < 4; i++) {
free(idx_list[i]);
free(val_list[i]);
}
}
}
free(freq);
return (ans == INT_MIN ? -1 : ans);
}
int main() {
char *s1 = "12233", *s2 = "1122211", *s3 = "110";
printf("%d\n", maxDifference(s1, 4)); // expect: -1
printf("%d\n", maxDifference(s2, 3)); // expect: 1
printf("%d\n", maxDifference(s3, 3)); // expect: -1
}
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