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52 lines
2.0 KiB
52 lines
2.0 KiB
2 months ago
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Binary search
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=============
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* <<defs,Definitions>>
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* <<examples,Examples>>
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!!ucw/binsearch.h
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[[examples]]
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Examples
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--------
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You can find few examples of binary search usage. Although we define only few macros, they can be used
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for several different cases, for example to find lower elements in a (non-)decreasing array or even to find
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elements in a (non-)increasing array.
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static int inc[10] = { 1, 4, 4, 5, 6, 10, 11, 20, 25, 50 };
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static const char *str[5] = { "aaa", "abc", "bflmpsvz", "rep", "rep" };
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static int dec[3] = { 5, 2, 1 };
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// find the first equal element
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printf("%d\n", BIN_SEARCH_EQ(inc, 10, 4)); // prints 1
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printf("%d\n", BIN_SEARCH_EQ(inc, 10, 15)); // prints -1 (not found)
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// find the first greater or equal element
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printf("%d\n", BIN_SEARCH_GE(inc, 10, 9)); // prints 5
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printf("%d\n", BIN_SEARCH_GE(inc, 10, 10)); // prints 5
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printf("%d\n", BIN_SEARCH_GE(inc, 10, 4)); // prints 1
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printf("%d\n", BIN_SEARCH_GE(inc, 10, 99)); // prints 10 (not found)
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// find the last equal element (or -1 if does not exist)
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#define CMP_LE(ary, i, x) ((ary[i]) <= (x))
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int i = BIN_SEARCH_FIRST_GE_CMP(inc, 10, 4, CMP_LE);
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printf("%d\n", (i && inc[i - 1] == 4) ? i - 1 : -1); // prints 2
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// find the first greater element
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printf("%d\n", BIN_SEARCH_FIRST_GE_CMP(inc, 10, 25, CMP_LE)); // prints 9
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// find the last lower or equal element (or -1 if does not exist)
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printf("%d\n", BIN_SEARCH_FIRST_GE_CMP(inc, 10, 25, CMP_LE) - 1); // prints 8
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// find the last lower element (or -1 if does not exist)
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printf("%d\n", BIN_SEARCH_FIRST_GE(inc, 10, 25) - 1); // prints 7
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// find the first greater or equal string
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#define CMP_STR(ary, i, x) (strcmp((ary[i]), (x)) < 0)
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printf("%d\n", BIN_SEARCH_GE_CMP(str, 5, "bfl", CMP_STR)); // prints 2
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// find the first lower or equal element in the non-increasing array
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#define CMP_GT(ary, i, x) ((ary[i]) > (x))
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printf("%d\n", BIN_SEARCH_FIRST_GE_CMP(dec, 3, 4, CMP_GT)); // prints 1
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