Created
October 18, 2020 14:18
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A five-color, in-place partitioning algorithm in O(n)-time (based on the Dutch flag algorithm).
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| enum Color { | |
| ORANGE, | |
| WHITE, | |
| RED, | |
| YELLOW, | |
| GREEN, | |
| }; | |
| void swap(enum Color *a, enum Color *b) { | |
| enum Color temp; | |
| temp = *a; | |
| *a = *b; | |
| *b = temp; | |
| } | |
| // https://stackoverflow.com/a/43015749 | |
| void jodhpur(enum Color *colors, int count) { | |
| int orange = 0; | |
| int white = 0; | |
| int red = 0; | |
| int yellow = 0; | |
| int green = count - 1; | |
| while (yellow <= green) { | |
| switch (colors[yellow]) { | |
| case ORANGE: | |
| swap(&colors[orange], &colors[yellow]); | |
| orange++; | |
| if (white < orange) { | |
| white++; | |
| } | |
| if (red < orange) { | |
| red++; | |
| } | |
| if (yellow < orange) { | |
| yellow++; | |
| } | |
| break; | |
| case WHITE: | |
| swap(&colors[white], &colors[yellow]); | |
| white++; | |
| if (red < white) { | |
| red++; | |
| } | |
| if (yellow < white) { | |
| yellow++; | |
| } | |
| break; | |
| case RED: | |
| swap(&colors[red], &colors[yellow]); | |
| red++; | |
| yellow++; | |
| break; | |
| case YELLOW: | |
| yellow++; | |
| break; | |
| case GREEN: | |
| swap(&colors[green], &colors[yellow]); | |
| green--; | |
| break; | |
| } | |
| } | |
| } |
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