mirror of https://github.com/TheAlgorithms/C
100 lines
2.7 KiB
C
100 lines
2.7 KiB
C
#include <stdio.h>
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#include <stdlib.h>
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int n, m; // size of the matrix
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// This function does Binary search for x in i-th row from j_low to j_high.
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void binarySearch(int **mat, int i, int j_low, int j_high, int x)
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{
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while (j_low <= j_high)
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{
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int j_mid = (j_low + j_high) / 2;
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// Element found
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if (mat[i][j_mid] == x)
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{
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printf("Found at (%d,%d)\n", i, j_mid);
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return;
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}
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else if (mat[i][j_mid] > x)
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j_high = j_mid - 1;
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else
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j_low = j_mid + 1;
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}
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// element not found
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printf("element not found\n");
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}
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// Function to perform binary search on the mid values of row to get the desired
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// pair of rows where the element can be found
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void modifiedBinarySearch(int **mat, int n, int m, int x)
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{ // If Single row matrix
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if (n == 1)
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{
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binarySearch(mat, 0, 0, m - 1, x);
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return;
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}
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// Do binary search in middle column.
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// Condition to terminate the loop when the 2 desired rows are found.
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int i_low = 0, i_high = n - 1, j_mid = m / 2;
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while ((i_low + 1) < i_high)
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{
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int i_mid = (i_low + i_high) / 2;
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// element found
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if (mat[i_mid][j_mid] == x)
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{
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printf("Found at (%d,%d)\n", i_mid, j_mid);
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return;
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}
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else if (mat[i_mid][j_mid] > x)
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i_high = i_mid;
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else
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i_low = i_mid;
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}
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// If element is present on the mid of the two rows
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if (mat[i_low][j_mid] == x)
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printf("Found at (%d,%d)\n", i_low, j_mid);
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else if (mat[i_low + 1][j_mid] == x)
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printf("Found at (%d,%d)\n", i_low + 1, j_mid);
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// Search element on 1st half of 1st row
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else if (x <= mat[i_low][j_mid - 1])
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binarySearch(mat, i_low, 0, j_mid - 1, x);
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// Search element on 2nd half of 1st row
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else if (x >= mat[i_low][j_mid + 1] && x <= mat[i_low][m - 1])
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binarySearch(mat, i_low, j_mid + 1, m - 1, x);
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// Search element on 1st half of 2nd row
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else if (x <= mat[i_low + 1][j_mid - 1])
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binarySearch(mat, i_low + 1, 0, j_mid - 1, x);
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// search element on 2nd half of 2nd row
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else
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binarySearch(mat, i_low + 1, j_mid + 1, m - 1, x);
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}
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int main()
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{
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int x; // element to be searched
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scanf("%d %d %d\n", &n, &m, &x);
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int **mat = (int **)malloc(n * sizeof(int *));
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for (x = 0; x < n; x++)
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mat[x] = (int *)malloc(m * sizeof(int));
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for (int i = 0; i < n; i++)
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{
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for (int j = 0; j < m; j++)
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{
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scanf("%d", &mat[i][j]);
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}
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}
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modifiedBinarySearch(mat, n, m, x);
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for (x = 0; x < n; x++)
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free(mat[x]);
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free(mat);
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return 0;
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}
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