Create 0179-largest-number.c

c/0179-largest-number.c

@@ -0,0 +1,45 @@
+// Compare two numbers in a concatenated form.
+// eg: 12 and 34 will be compared as 1234 vs 3412
+int compareInt(const void *a, const void *b) {
+    int i = 10;
+    int j = 10;
+    int x = *(int*)a;
+    int y = *(int*)b;
+
+    while (x /= 10) i *= 10;
+    while (y /= 10) j *= 10;
+
+    return  (((unsigned int)*(int*)b * i) + *(int*)a) > (((unsigned int)*(int*)a * j) + *(int*)b);
+}
+
+char * largestNumber(int* nums, int numsSize){
+    char *res = NULL;
+    int i, len, pos;
+
+    if (numsSize < 0) {
+        return res;
+    }
+
+    // Sort the array with specified comparaotor.
+    qsort(nums, numsSize, sizeof(int), compareInt);
+
+    // Caculate the length of the return string.
+    len = 1;
+    for (i = 0; i < numsSize; i++) len +=  snprintf(NULL, 0, "%d", nums[i]);
+    res = calloc(len, sizeof(char));
+
+    // If the firs element of sorted array is 0,
+    // return a single digit of 0 no matter how long is the string.
+    if (nums[0] == 0) {
+        res[0] = '0';
+        return res;
+    }
+
+    // Print all nums to the return string.
+    pos = 0;
+    for (i = 0; i < numsSize; i++) {
+        pos += snprintf(res + pos, len, "%d", nums[i]);
+    }
+
+    return res;
+}