diff --git a/056_merge_intervals/Makefile b/056_merge_intervals/Makefile
new file mode 100644
index 0000000..9b568bc
--- /dev/null
+++ b/056_merge_intervals/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test merge_intervals.c
diff --git a/056_merge_intervals/merge_intervals.c b/056_merge_intervals/merge_intervals.c
new file mode 100644
index 0000000..a07096d
--- /dev/null
+++ b/056_merge_intervals/merge_intervals.c
@@ -0,0 +1,151 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Interval {
+    int start;
+    int end;
+};
+
+static int binary_search(int *nums, int size, int target)
+{
+    int low = -1;
+    int high = size;
+    while (low + 1 < high) {
+        int mid = low + (high - low) / 2;
+        if (target > nums[mid]) {
+            low = mid;
+        } else {
+            high = mid;
+        }
+    }
+    if (high == size || nums[high] != target) {
+        return -high - 1;
+    } else {
+        return high;
+    }
+}
+
+/**
+ ** Return an array of size *returnSize.
+ ** Note: The returned array must be malloced, assume caller calls free().
+ **/
+static struct Interval* insert(struct Interval* intervals, int intervalsSize, struct Interval newInterval, int* returnSize)
+{
+    struct Interval *p;
+    if (intervalsSize == 0) {
+        p = malloc(sizeof(*p));
+        p->start = newInterval.start;
+        p->end = newInterval.end;
+        *returnSize = 1;
+        return p;
+    }
+
+    int i, count;
+    int *nums = malloc(2 * intervalsSize * sizeof(int));
+    for (i = 0; i < intervalsSize; i++) {
+        nums[i * 2] = intervals[i].start;
+        nums[i * 2 + 1] = intervals[i].end;
+    }
+
+    int start0 = binary_search(nums, 2 * intervalsSize, newInterval.start);
+    int end0 = binary_search(nums, 2 * intervalsSize, newInterval.end);
+
+    int start1 = -1, end1 = -1;
+    int merge_start= -1, merge_end = -1;
+    if (start0 >= 0) {
+        merge_start = start0 / 2;
+    } else {
+        start1 = -start0 - 1;
+        merge_start = start1 / 2;
+    }
+
+    if (end0 >= 0) {
+        merge_end = end0 / 2;
+    } else {
+        end1 = -end0 - 1;
+        if (end1 % 2 == 0) {
+            merge_end = end1 / 2 > 0 ? end1 / 2 - 1 : 0;
+        } else {
+            merge_end = end1 / 2;
+        }
+    }
+
+    if (merge_start == merge_end) {
+        if (start0 < 0 && end0 < 0 && start1 == end1 && start1 % 2 == 0) {
+            count = intervalsSize + 1;
+            p = malloc(count * sizeof(*p));
+            memcpy(p, intervals, merge_start * sizeof(*p));
+            p[merge_start] = newInterval;
+            memcpy(p + merge_start + 1, intervals + merge_start, (intervalsSize - merge_start) * sizeof(*p));
+        } else {
+            count = intervalsSize;
+            p = malloc(count * sizeof(*p));
+            memcpy(p, intervals, count * sizeof(*p));
+            if (start0 < 0 && start1 % 2 == 0) {
+                p[merge_start].start = newInterval.start;
+            }
+            if (end0 < 0 && end1 % 2 == 0) {
+                p[merge_end].end = newInterval.end;
+            }
+        }
+    } else {
+        count = intervalsSize - (merge_end - merge_start);
+        p = malloc(count * sizeof(*p));
+        memcpy(p, intervals, merge_start * sizeof(*p));
+        memcpy(p + merge_start, intervals + merge_end, (intervalsSize - merge_end) * sizeof(*p));
+        if (start0 < 0 && start1 % 2 == 0) {
+            p[merge_start].start = newInterval.start;
+        } else {
+            p[merge_start].start = intervals[merge_start].start;
+        }
+        if (end0 < 0 && end1 % 2 == 0) {
+            p[merge_start].end = newInterval.end;
+        } else {
+            p[merge_start].end = intervals[merge_end].end;
+        }
+    }
+
+    free(nums);
+    free(intervals);
+    *returnSize = count;
+    return p;
+}
+
+/**
+ *  * Return an array of size *returnSize.
+ *   * Note: The returned array must be malloced, assume caller calls free().
+ *    */
+struct Interval* merge(struct Interval* intervals, int intervalsSize, int* returnSize) {
+    int i, count = 0;
+    struct Interval *p = NULL;
+    for (i = 0; i < intervalsSize; i++) {
+        p = insert(p, count, intervals[i], &count);
+    }
+    *returnSize = count;
+    return p;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc < 1|| argc % 2 == 0) {
+        fprintf(stderr, "Usage: ./test s0 e0 s1 e1...");
+        exit(-1);
+    }
+
+    int i, count = 0;
+    struct Interval *intervals = malloc((argc - 1) / 2 * sizeof(struct Interval));
+    struct Interval *p = intervals;
+    for (i = 1; i < argc; i += 2) {
+        p->start = atoi(argv[i]);
+        p->end = atoi(argv[i + 1]);
+        p++;
+    }
+
+    struct Interval *q = merge(intervals, (argc - 1) / 2, &count);
+    for (i = 0; i < count; i++) {
+        printf("[%d, %d]\n", q->start, q->end);
+        q++;
+    }
+    return 0;
+}
diff --git a/057_insert_interval/Makefile b/057_insert_interval/Makefile
new file mode 100644
index 0000000..bc9dd24
--- /dev/null
+++ b/057_insert_interval/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test insert_interval.c
diff --git a/057_insert_interval/insert_interval.c b/057_insert_interval/insert_interval.c
new file mode 100644
index 0000000..fd29352
--- /dev/null
+++ b/057_insert_interval/insert_interval.c
@@ -0,0 +1,139 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+struct Interval {
+    int start;
+    int end;
+};
+
+static int binary_search(int *nums, int size, int target)
+{
+    int low = -1;
+    int high = size;
+    while (low + 1 < high) {
+        int mid = low + (high - low) / 2;
+        if (target > nums[mid]) {
+            low = mid;
+        } else {
+            high = mid;
+        }
+    }
+    if (high == size || nums[high] != target) {
+        return -high - 1;
+    } else {
+        return high;
+    }
+}
+
+/**
+ ** Return an array of size *returnSize.
+ ** Note: The returned array must be malloced, assume caller calls free().
+ **/
+static struct Interval* insert(struct Interval* intervals, int intervalsSize, struct Interval newInterval, int* returnSize) {
+    struct Interval *p;
+    if (intervalsSize == 0) {
+        p = malloc(sizeof(*p));
+        p->start = newInterval.start;
+        p->end = newInterval.end;
+        *returnSize = 1;
+        return p;
+    }
+
+    int i, count;
+    int *nums = malloc(2 * intervalsSize * sizeof(int));
+    for (i = 0; i < intervalsSize; i++) {
+        nums[i * 2] = intervals[i].start;
+        nums[i * 2 + 1] = intervals[i].end;
+    }
+
+    int start0 = binary_search(nums, 2 * intervalsSize, newInterval.start);
+    int end0 = binary_search(nums, 2 * intervalsSize, newInterval.end);
+
+    int start1 = -1, end1 = -1;
+    int merge_start= -1, merge_end = -1;
+    if (start0 >= 0) {
+        merge_start = start0 / 2;
+    } else {
+        start1 = -start0 - 1;
+        merge_start = start1 / 2;
+    }
+
+    if (end0 >= 0) {
+        merge_end = end0 / 2;
+    } else {
+        end1 = -end0 - 1;
+        if (end1 % 2 == 0) {
+            merge_end = end1 / 2 > 0 ? end1 / 2 - 1 : 0;
+        } else {
+            merge_end = end1 / 2;
+        }
+    }
+
+    if (merge_start == merge_end) {
+        if (start0 < 0 && end0 < 0 && start1 == end1 && start1 % 2 == 0) {
+            count = intervalsSize + 1;
+            p = malloc(count * sizeof(*p));
+            memcpy(p, intervals, merge_start * sizeof(*p));
+            p[merge_start] = newInterval;
+            memcpy(p + merge_start + 1, intervals + merge_start, (intervalsSize - merge_start) * sizeof(*p));
+        } else {
+            count = intervalsSize;
+            p = malloc(count * sizeof(*p));
+            memcpy(p, intervals, count * sizeof(*p));
+            if (start0 < 0 && start1 % 2 == 0) {
+                p[merge_start].start = newInterval.start;
+            }
+            if (end0 < 0 && end1 % 2 == 0) {
+                p[merge_end].end = newInterval.end;
+            }
+        }
+    } else {
+        count = intervalsSize - (merge_end - merge_start);
+        p = malloc(count * sizeof(*p));
+        memcpy(p, intervals, merge_start * sizeof(*p));
+        memcpy(p + merge_start, intervals + merge_end, (intervalsSize - merge_end) * sizeof(*p));
+        if (start0 < 0 && start1 % 2 == 0) {
+            p[merge_start].start = newInterval.start;
+        } else {
+            p[merge_start].start = intervals[merge_start].start;
+        }
+        if (end0 < 0 && end1 % 2 == 0) {
+            p[merge_start].end = newInterval.end;
+        } else {
+            p[merge_start].end = intervals[merge_end].end;
+        }
+    }
+
+    free(nums);
+    *returnSize = count;
+    return p;
+}
+
+int main(int argc, char **argv)
+{
+    if (argc < 3 || argc % 2 == 0) {
+        fprintf(stderr, "Usage: ./test new_s new_e s0 e0 s1 e1...");
+        exit(-1);
+    }
+
+    struct Interval new_interv;
+    new_interv.start = atoi(argv[1]);
+    new_interv.end = atoi(argv[2]);
+
+    int i, count = 0;
+    struct Interval *intervals = malloc((argc - 3) / 2 * sizeof(struct Interval));
+    struct Interval *p = intervals;
+    for (i = 3; i < argc; i += 2) {
+        p->start = atoi(argv[i]);
+        p->end = atoi(argv[i + 1]);
+        p++;
+    }
+
+    struct Interval *q = insert(intervals, (argc - 3) / 2, new_interv, &count);
+    for (i = 0; i < count; i++) {
+        printf("[%d, %d]\n", q->start, q->end);
+        q++;
+    }
+    return 0;
+}