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+/*
+Challenge 137
+
+TASK #1 > Long Year
+Submitted by: Mohammad S Anwar
+Write a script to find all the years between 1900 and 2100 which is a Long
+Year.
+
+A year is Long if it has 53 weeks.
+
+
+[UPDATED][2021-11-01 16:20:00]: For more information about Long Year, please
+refer to wikipedia.
+
+Expected Output
+1903, 1908, 1914, 1920, 1925,
+1931, 1936, 1942, 1948, 1953,
+1959, 1964, 1970, 1976, 1981,
+1987, 1992, 1998, 2004, 2009,
+2015, 2020, 2026, 2032, 2037,
+2043, 2048, 2054, 2060, 2065,
+2071, 2076, 2082, 2088, 2093,
+2099
+
+https://en.wikipedia.org/wiki/ISO_week_date#Weeks_per_year
+years in which 1 January or 31 December are Thursdays
+*/
+
+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+
+enum { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday };
+
+int day_of_week(int y, int m, int d) {
+    return (d += m < 3 ? y-- : y - 2, 23*m/9 + d + 4 + y/4- y/100 + y/400)%7;
+}
+
+bool is_long_year(int y) {
+    if (day_of_week(y,1,1) == Thursday || day_of_week(y,12,31) == Thursday)
+        return true;
+    else
+        return false;
+}
+
+int main() {
+    int col = 0;
+    const char* sep = "";
+    for (int y = 1900; y <= 2100; y++) {
+        if (is_long_year(y)) {
+            printf("%s%d", sep, y);
+            sep = ", ";
+            col++;
+            if (col == 5) {
+                col = 0;
+                sep = ",\n";
+            }
+        }
+    }
+    printf("\n");
+}